// Written in the D programming language.

/++
    This module defines functions related to exceptions and general error
    handling. It also defines functions intended to aid in unit testing.

    Synopsis of some of std.exception's functions:
    --------------------
    string synopsis()
    {
        FILE* f = enforce(fopen("some/file"));
        // f is not null from here on
        FILE* g = enforce!WriteException(fopen("some/other/file", "w"));
        // g is not null from here on

        Exception e = collectException(write(g, readln(f)));
        if (e)
        {
            ... an exception occurred...
            ... We have the exception to play around with...
        }

        string msg = collectExceptionMsg(write(g, readln(f)));
        if (msg)
        {
            ... an exception occurred...
            ... We have the message from the exception but not the exception...
        }

        char[] line;
        enforce(readln(f, line));
        return assumeUnique(line);
    }
    --------------------

    Macros:
        WIKI = Phobos/StdException

    Copyright: Copyright Andrei Alexandrescu 2008-, Jonathan M Davis 2011-.
    License:   $(WEB boost.org/LICENSE_1_0.txt, Boost License 1.0)
    Authors:   $(WEB erdani.org, Andrei Alexandrescu) and Jonathan M Davis
    Source:    $(PHOBOSSRC std/_exception.d)

 +/
module std.exception;

import std.range;
import std.traits;

import core.stdc.errno;
import core.stdc.string;

/++
    Asserts that the given expression does $(I not) throw the given type
    of $(D Throwable). If a $(D Throwable) of the given type is thrown,
    it is caught and does not escape assertNotThrown. Rather, an
    $(D AssertError) is thrown. However, any other $(D Throwable)s will escape.

    Params:
        T          = The $(D Throwable) to test for.
        expression = The expression to test.
        msg        = Optional message to output on test failure.
                     If msg is empty, and the thrown exception has a
                     non-empty msg field, the exception's msg field
                     will be output on test failure.
        file       = The file where the error occurred.
                     Defaults to $(D __FILE__).
        line       = The line where the error occurred.
                     Defaults to $(D __LINE__).

    Throws:
        $(D AssertError) if the given $(D Throwable) is thrown.

    Returns:
        the result of `expression`.
 +/
auto assertNotThrown(T : Throwable = Exception, E)
                    (lazy E expression,
                     string msg = null,
                     string file = __FILE__,
                     size_t line = __LINE__)
{
    import core.exception : AssertError;
    try
    {
        return expression();
    }
    catch (T t)
    {
        immutable message = msg.length == 0 ? t.msg : msg;
        immutable tail = message.length == 0 ? "." : ": " ~ message;
        throw new AssertError("assertNotThrown failed: " ~ T.stringof ~ " was thrown" ~ tail, file, line, t);
    }
}
///
unittest
{
    import core.exception : AssertError;

    import std.string;
    assertNotThrown!StringException(enforce!StringException(true, "Error!"));

    //Exception is the default.
    assertNotThrown(enforce!StringException(true, "Error!"));

    assert(collectExceptionMsg!AssertError(assertNotThrown!StringException(
               enforce!StringException(false, "Error!"))) ==
           `assertNotThrown failed: StringException was thrown: Error!`);
}
unittest
{
    import core.exception : AssertError;
    import std.string;
    assert(collectExceptionMsg!AssertError(assertNotThrown!StringException(
               enforce!StringException(false, ""), "Error!")) ==
           `assertNotThrown failed: StringException was thrown: Error!`);

    assert(collectExceptionMsg!AssertError(assertNotThrown!StringException(
               enforce!StringException(false, ""))) ==
           `assertNotThrown failed: StringException was thrown.`);

    assert(collectExceptionMsg!AssertError(assertNotThrown!StringException(
               enforce!StringException(false, ""), "")) ==
           `assertNotThrown failed: StringException was thrown.`);
}

unittest
{
    import core.exception : AssertError;

    void throwEx(Throwable t) { throw t; }
    bool nothrowEx() { return true; }

    try
    {
        assert(assertNotThrown!Exception(nothrowEx()));
    }
    catch (AssertError) assert(0);

    try
    {
        assert(assertNotThrown!Exception(nothrowEx(), "It's a message"));
    }
    catch (AssertError) assert(0);

    try
    {
        assert(assertNotThrown!AssertError(nothrowEx()));
    }
    catch (AssertError) assert(0);

    try
    {
        assert(assertNotThrown!AssertError(nothrowEx(), "It's a message"));
    }
    catch (AssertError) assert(0);

    {
        bool thrown = false;
        try
        {
            assertNotThrown!Exception(
                throwEx(new Exception("It's an Exception")));
        }
        catch (AssertError) thrown = true;
        assert(thrown);
    }

    {
        bool thrown = false;
        try
        {
            assertNotThrown!Exception(
                throwEx(new Exception("It's an Exception")), "It's a message");
        }
        catch (AssertError) thrown = true;
        assert(thrown);
    }

    {
        bool thrown = false;
        try
        {
            assertNotThrown!AssertError(
                throwEx(new AssertError("It's an AssertError", __FILE__, __LINE__)));
        }
        catch (AssertError) thrown = true;
        assert(thrown);
    }

    {
        bool thrown = false;
        try
        {
            assertNotThrown!AssertError(
                throwEx(new AssertError("It's an AssertError", __FILE__, __LINE__)),
                        "It's a message");
        }
        catch (AssertError) thrown = true;
        assert(thrown);
    }
}

/++
    Asserts that the given expression throws the given type of $(D Throwable).
    The $(D Throwable) is caught and does not escape assertThrown. However,
    any other $(D Throwable)s $(I will) escape, and if no $(D Throwable)
    of the given type is thrown, then an $(D AssertError) is thrown.

    Params:
        T          = The $(D Throwable) to test for.
        expression = The expression to test.
        msg        = Optional message to output on test failure.
        file       = The file where the error occurred.
                     Defaults to $(D __FILE__).
        line       = The line where the error occurred.
                     Defaults to $(D __LINE__).

    Throws:
        $(D AssertError) if the given $(D Throwable) is not thrown.
  +/
void assertThrown(T : Throwable = Exception, E)
                 (lazy E expression,
                  string msg = null,
                  string file = __FILE__,
                  size_t line = __LINE__)
{
    import core.exception : AssertError;

    try
        expression();
    catch (T)
        return;
    throw new AssertError("assertThrown failed: No " ~ T.stringof ~ " was thrown"
                                 ~ (msg.length == 0 ? "." : ": ") ~ msg,
                          file, line);
}
///
unittest
{
    import core.exception : AssertError;
    import std.string;

    assertThrown!StringException(enforce!StringException(false, "Error!"));

    //Exception is the default.
    assertThrown(enforce!StringException(false, "Error!"));

    assert(collectExceptionMsg!AssertError(assertThrown!StringException(
               enforce!StringException(true, "Error!"))) ==
           `assertThrown failed: No StringException was thrown.`);
}

unittest
{
    import core.exception : AssertError;

    void throwEx(Throwable t) { throw t; }
    void nothrowEx() { }

    try
    {
        assertThrown!Exception(throwEx(new Exception("It's an Exception")));
    }
    catch (AssertError) assert(0);

    try
    {
        assertThrown!Exception(throwEx(new Exception("It's an Exception")),
                               "It's a message");
    }
    catch(AssertError) assert(0);

    try
    {
        assertThrown!AssertError(throwEx(new AssertError("It's an AssertError",
                                                         __FILE__, __LINE__)));
    }
    catch (AssertError) assert(0);

    try
    {
        assertThrown!AssertError(throwEx(new AssertError("It's an AssertError",
                                                         __FILE__, __LINE__)),
                                 "It's a message");
    }
    catch (AssertError) assert(0);


    {
        bool thrown = false;
        try
            assertThrown!Exception(nothrowEx());
        catch(AssertError)
            thrown = true;

        assert(thrown);
    }

    {
        bool thrown = false;
        try
            assertThrown!Exception(nothrowEx(), "It's a message");
        catch(AssertError)
            thrown = true;

        assert(thrown);
    }

    {
        bool thrown = false;
        try
            assertThrown!AssertError(nothrowEx());
        catch(AssertError)
            thrown = true;

        assert(thrown);
    }

    {
        bool thrown = false;
        try
            assertThrown!AssertError(nothrowEx(), "It's a message");
        catch(AssertError)
            thrown = true;

        assert(thrown);
    }
}


/++
    Enforces that the given value is true.

    Params:
        value = The value to test.
        E = Exception type to throw if the value evalues to false.
        msg = The error message to put in the exception if it is thrown.
        file = The source file of the caller.
        line = The line number of the caller.

    Returns: $(D value), if `cast(bool)value` is true. Otherwise,
    $(D new Exception(msg)) is thrown.

    Note:
        $(D enforce) is used to throw exceptions and is therefore intended to
        aid in error handling. It is $(I not) intended for verifying the logic
        of your program. That is what $(D assert) is for. Also, do not use
        $(D enforce) inside of contracts (i.e. inside of $(D in) and $(D out)
        blocks and $(D invariant)s), because they will be compiled out when
        compiling with $(I -release). Use $(D assert) in contracts.

    Example:
    --------------------
    auto f = enforce(fopen("data.txt"));
    auto line = readln(f);
    enforce(line.length, "Expected a non-empty line.");
    --------------------
 +/
T enforce(E : Throwable = Exception, T)(T value, lazy const(char)[] msg = null, string file = __FILE__, size_t line = __LINE__)
    if (is(typeof({ if (!value) {} })))
{
    if (!value) bailOut!E(file, line, msg);
    return value;
}

// Explicitly undocumented. It will be removed in August 2016. @@@DEPRECATED_2016-08@@@
deprecated("Use the overload of enforce that takes file and line as function arguments.")
T enforce(T, string file, size_t line = __LINE__)
    (T value, lazy const(char)[] msg = null)
    if (is(typeof({ if (!value) {} })))
{
    if (!value) bailOut(file, line, msg);
    return value;
}

/++
    Enforces that the given value is true.

    Params:
        value = The value to test.
        dg = The delegate to be called if the value evaluates to false.
        file = The source file of the caller.
        line = The line number of the caller.

    Returns: $(D value), if `cast(bool)value` is true. Otherwise, the given
    delegate is called.

    The safety and purity of this function are inferred from $(D Dg)'s safety
    and purity.
 +/
T enforce(T, Dg, string file = __FILE__, size_t line = __LINE__)
    (T value, scope Dg dg)
    if (isSomeFunction!Dg && is(typeof( dg() )) &&
        is(typeof({ if (!value) {} })))
{
    if (!value) dg();
    return value;
}

private void bailOut(E : Throwable = Exception)(string file, size_t line, in char[] msg)
{
    static if (is(typeof(new E(string.init, string.init, size_t.init))))
    {
        throw new E(msg.ptr ? msg.idup : "Enforcement failed", file, line);
    }
    else static if (is(typeof(new E(string.init, size_t.init))))
    {
        throw new E(file, line);
    }
    else
    {
        static assert(0, "Expected this(string, string, size_t) or this(string, size_t)" ~
            " constructor for " ~ __traits(identifier, E));
    }
}

unittest
{
    assert (enforce(123) == 123);

    try
    {
        enforce(false, "error");
        assert (false);
    }
    catch (Exception e)
    {
        assert (e.msg == "error");
        assert (e.file == __FILE__);
        assert (e.line == __LINE__-7);
    }
}

unittest
{
    // Issue 10510
    extern(C) void cFoo() { }
    enforce(false, &cFoo);
}

// purity and safety inference test
unittest
{
    import std.meta : AliasSeq;

    foreach (EncloseSafe; AliasSeq!(false, true))
    foreach (EnclosePure; AliasSeq!(false, true))
    {
        foreach (BodySafe; AliasSeq!(false, true))
        foreach (BodyPure; AliasSeq!(false, true))
        {
            enum code =
                "delegate void() " ~
                (EncloseSafe ? "@safe " : "") ~
                (EnclosePure ? "pure " : "") ~
                "{ enforce(true, { " ~
                        "int n; " ~
                        (BodySafe ? "" : "auto p = &n + 10; "    ) ~    // unsafe code
                        (BodyPure ? "" : "static int g; g = 10; ") ~    // impure code
                    "}); " ~
                "}";
            enum expect =
                (BodySafe || !EncloseSafe) && (!EnclosePure || BodyPure);

            version(none)
            pragma(msg, "safe = ", EncloseSafe?1:0, "/", BodySafe?1:0, ", ",
                        "pure = ", EnclosePure?1:0, "/", BodyPure?1:0, ", ",
                        "expect = ", expect?"OK":"NG", ", ",
                        "code = ", code);

            static assert(__traits(compiles, mixin(code)()) == expect);
        }
    }
}

// Test for bugzilla 8637
unittest
{
    struct S
    {
        static int g;
        ~this() {}  // impure & unsafe destructor
        bool opCast(T:bool)() {
            int* p = cast(int*)0;   // unsafe operation
            int n = g;              // impure operation
            return true;
        }
    }
    S s;

    enforce(s);
    enforce(s, {});
    enforce(s, new Exception(""));

    errnoEnforce(s);

    alias E1 = Exception;
    static class E2 : Exception
    {
        this(string fn, size_t ln) { super("", fn, ln); }
    }
    static class E3 : Exception
    {
        this(string msg) { super(msg, __FILE__, __LINE__); }
    }
    enforce!E1(s);
    enforce!E2(s);
}

deprecated unittest
{
    struct S
    {
        static int g;
        ~this() {}  // impure & unsafe destructor
        bool opCast(T:bool)() {
            int* p = cast(int*)0;   // unsafe operation
            int n = g;              // impure operation
            return true;
        }
    }
    S s;

    enforce!(S, __FILE__, __LINE__)(s, "");
}

unittest
{
    // Issue 14685

    class E : Exception
    {
        this() { super("Not found"); }
    }
    static assert(!__traits(compiles, { enforce!E(false); }));
}

/++
    Enforces that the given value is true.

    Params:
        value = The value to test.
        ex = The exception to throw if the value evaluates to false.

    Returns: $(D value), if `cast(bool)value` is true. Otherwise, $(D ex) is
    thrown.

    Example:
    --------------------
    auto f = enforce(fopen("data.txt"));
    auto line = readln(f);
    enforce(line.length, new IOException); // expect a non-empty line
    --------------------
 +/
T enforce(T)(T value, lazy Throwable ex)
{
    if (!value) throw ex();
    return value;
}

unittest
{
    assertNotThrown(enforce(true, new Exception("this should not be thrown")));
    assertThrown(enforce(false, new Exception("this should be thrown")));
}

/++
    Enforces that the given value is true, throwing an `ErrnoException` if it
    is not.

    Params:
        value = The value to test.
        msg = The message to include in the `ErrnoException` if it is thrown.

    Returns: $(D value), if `cast(bool)value` is true. Otherwise,
    $(D new ErrnoException(msg)) is thrown.  It is assumed that the last
    operation set $(D errno) to an error code corresponding with the failed
    condition.

    Example:
    --------------------
    auto f = errnoEnforce(fopen("data.txt"));
    auto line = readln(f);
    enforce(line.length); // expect a non-empty line
    --------------------
 +/
T errnoEnforce(T, string file = __FILE__, size_t line = __LINE__)
    (T value, lazy string msg = null)
{
    if (!value) throw new ErrnoException(msg, file, line);
    return value;
}


/++
    If $(D !value) is $(D false), $(D value) is returned. Otherwise,
    $(D new E(msg, file, line)) is thrown. Or if $(D E) doesn't take a message
    and can be constructed with $(D new E(file, line)), then
    $(D new E(file, line)) will be thrown.

    This is legacy name, it is recommended to use $(D enforce!E) instead.

    Example:
    --------------------
    auto f = enforceEx!FileMissingException(fopen("data.txt"));
    auto line = readln(f);
    enforceEx!DataCorruptionException(line.length);
    --------------------
 +/
template enforceEx(E : Throwable)
    if (is(typeof(new E("", __FILE__, __LINE__))))
{
    /++ Ditto +/
    T enforceEx(T)(T value, lazy string msg = "", string file = __FILE__, size_t line = __LINE__)
    {
        if (!value) throw new E(msg, file, line);
        return value;
    }
}

/++ Ditto +/
template enforceEx(E : Throwable)
    if (is(typeof(new E(__FILE__, __LINE__))) && !is(typeof(new E("", __FILE__, __LINE__))))
{
    /++ Ditto +/
    T enforceEx(T)(T value, string file = __FILE__, size_t line = __LINE__)
    {
        if (!value) throw new E(file, line);
        return value;
    }
}

unittest
{
    import std.array : empty;
    import core.exception : OutOfMemoryError;
    assertNotThrown(enforceEx!Exception(true));
    assertNotThrown(enforceEx!Exception(true, "blah"));
    assertNotThrown(enforceEx!OutOfMemoryError(true));

    {
        auto e = collectException(enforceEx!Exception(false));
        assert(e !is null);
        assert(e.msg.empty);
        assert(e.file == __FILE__);
        assert(e.line == __LINE__ - 4);
    }

    {
        auto e = collectException(enforceEx!Exception(false, "hello", "file", 42));
        assert(e !is null);
        assert(e.msg == "hello");
        assert(e.file == "file");
        assert(e.line == 42);
    }

    {
        auto e = collectException!Error(enforceEx!OutOfMemoryError(false));
        assert(e !is null);
        assert(e.msg == "Memory allocation failed");
        assert(e.file == __FILE__);
        assert(e.line == __LINE__ - 4);
    }

    {
        auto e = collectException!Error(enforceEx!OutOfMemoryError(false, "file", 42));
        assert(e !is null);
        assert(e.msg == "Memory allocation failed");
        assert(e.file == "file");
        assert(e.line == 42);
    }

    static assert(!is(typeof(enforceEx!int(true))));
}

unittest
{
    alias enf = enforceEx!Exception;
    assertNotThrown(enf(true));
    assertThrown(enf(false, "blah"));
}


/++
    Catches and returns the exception thrown from the given expression.
    If no exception is thrown, then null is returned and $(D result) is
    set to the result of the expression.

    Note that while $(D collectException) $(I can) be used to collect any
    $(D Throwable) and not just $(D Exception)s, it is generally ill-advised to
    catch anything that is neither an $(D Exception) nor a type derived from
    $(D Exception). So, do not use $(D collectException) to collect
    non-$(D Exception)s unless you're sure that that's what you really want to
    do.

    Params:
        T          = The type of exception to catch.
        expression = The expression which may throw an exception.
        result     = The result of the expression if no exception is thrown.
+/
T collectException(T = Exception, E)(lazy E expression, ref E result)
{
    try
    {
        result = expression();
    }
    catch (T e)
    {
        return e;
    }
    return null;
}
///
unittest
{
    int b;
    int foo() { throw new Exception("blah"); }
    assert(collectException(foo(), b));

    int[] a = new int[3];
    import core.exception : RangeError;
    assert(collectException!RangeError(a[4], b));
}

/++
    Catches and returns the exception thrown from the given expression.
    If no exception is thrown, then null is returned. $(D E) can be
    $(D void).

    Note that while $(D collectException) $(I can) be used to collect any
    $(D Throwable) and not just $(D Exception)s, it is generally ill-advised to
    catch anything that is neither an $(D Exception) nor a type derived from
    $(D Exception). So, do not use $(D collectException) to collect
    non-$(D Exception)s unless you're sure that that's what you really want to
    do.

    Params:
        T          = The type of exception to catch.
        expression = The expression which may throw an exception.
+/
T collectException(T : Throwable = Exception, E)(lazy E expression)
{
    try
    {
        expression();
    }
    catch (T t)
    {
        return t;
    }
    return null;
}

unittest
{
    int foo() { throw new Exception("blah"); }
    assert(collectException(foo()));
}

/++
    Catches the exception thrown from the given expression and returns the
    msg property of that exception. If no exception is thrown, then null is
    returned. $(D E) can be $(D void).

    If an exception is thrown but it has an empty message, then
    $(D emptyExceptionMsg) is returned.

    Note that while $(D collectExceptionMsg) $(I can) be used to collect any
    $(D Throwable) and not just $(D Exception)s, it is generally ill-advised to
    catch anything that is neither an $(D Exception) nor a type derived from
    $(D Exception). So, do not use $(D collectExceptionMsg) to collect
    non-$(D Exception)s unless you're sure that that's what you really want to
    do.

    Params:
        T          = The type of exception to catch.
        expression = The expression which may throw an exception.
+/
string collectExceptionMsg(T = Exception, E)(lazy E expression)
{
    import std.array : empty;
    try
    {
        expression();

        return cast(string)null;
    }
    catch(T e)
        return e.msg.empty ? emptyExceptionMsg : e.msg;
}
///
unittest
{
    void throwFunc() { throw new Exception("My Message."); }
    assert(collectExceptionMsg(throwFunc()) == "My Message.");

    void nothrowFunc() {}
    assert(collectExceptionMsg(nothrowFunc()) is null);

    void throwEmptyFunc() { throw new Exception(""); }
    assert(collectExceptionMsg(throwEmptyFunc()) == emptyExceptionMsg);
}

/++
    Value that collectExceptionMsg returns when it catches an exception
    with an empty exception message.
 +/
enum emptyExceptionMsg = "<Empty Exception Message>";

/**
 * Casts a mutable array to an immutable array in an idiomatic
 * manner. Technically, $(D assumeUnique) just inserts a cast,
 * but its name documents assumptions on the part of the
 * caller. $(D assumeUnique(arr)) should only be called when
 * there are no more active mutable aliases to elements of $(D
 * arr). To strengthen this assumption, $(D assumeUnique(arr))
 * also clears $(D arr) before returning. Essentially $(D
 * assumeUnique(arr)) indicates commitment from the caller that there
 * is no more mutable access to any of $(D arr)'s elements
 * (transitively), and that all future accesses will be done through
 * the immutable array returned by $(D assumeUnique).
 *
 * Typically, $(D assumeUnique) is used to return arrays from
 * functions that have allocated and built them.
 *
 * Params:
 *  array = The array to cast to immutable.
 *
 * Returns: The immutable array.
 *
 * Example:
 *
 * ----
 * string letters()
 * {
 *   char[] result = new char['z' - 'a' + 1];
 *   foreach (i, ref e; result)
 *   {
 *     e = cast(char)('a' + i);
 *   }
 *   return assumeUnique(result);
 * }
 * ----
 *
 * The use in the example above is correct because $(D result)
 * was private to $(D letters) and is inaccessible in writing
 * after the function returns. The following example shows an
 * incorrect use of $(D assumeUnique).
 *
 * Bad:
 *
 * ----
 * private char[] buffer;
 * string letters(char first, char last)
 * {
 *   if (first >= last) return null; // fine
 *   auto sneaky = buffer;
 *   sneaky.length = last - first + 1;
 *   foreach (i, ref e; sneaky)
 *   {
 *     e = cast(char)('a' + i);
 *   }
 *   return assumeUnique(sneaky); // BAD
 * }
 * ----
 *
 * The example above wreaks havoc on client code because it is
 * modifying arrays that callers considered immutable. To obtain an
 * immutable array from the writable array $(D buffer), replace
 * the last line with:
 * ----
 * return to!(string)(sneaky); // not that sneaky anymore
 * ----
 *
 * The call will duplicate the array appropriately.
 *
 * Note that checking for uniqueness during compilation is
 * possible in certain cases, especially when a function is
 * marked as a pure function. The following example does not
 * need to call assumeUnique because the compiler can infer the
 * uniqueness of the array in the pure function:
 * ----
 * string letters() pure
 * {
 *   char[] result = new char['z' - 'a' + 1];
 *   foreach (i, ref e; result)
 *   {
 *     e = cast(char)('a' + i);
 *   }
 *   return result;
 * }
 * ----
 *
 * For more on infering uniqueness see the $(B unique) and
 * $(B lent) keywords in the
 * $(WEB archjava.fluid.cs.cmu.edu/papers/oopsla02.pdf, ArchJava)
 * language.
 *
 * The downside of using $(D assumeUnique)'s
 * convention-based usage is that at this time there is no
 * formal checking of the correctness of the assumption;
 * on the upside, the idiomatic use of $(D assumeUnique) is
 * simple and rare enough to be tolerable.
 *
 */
immutable(T)[] assumeUnique(T)(T[] array) pure nothrow
{
    return .assumeUnique(array);    // call ref version
}
/// ditto
immutable(T)[] assumeUnique(T)(ref T[] array) pure nothrow
{
    auto result = cast(immutable(T)[]) array;
    array = null;
    return result;
}

unittest
{
    int[] arr = new int[1];
    auto arr1 = assumeUnique(arr);
    assert(is(typeof(arr1) == immutable(int)[]) && arr == null);
}

immutable(T[U]) assumeUnique(T, U)(ref T[U] array) pure nothrow
{
    auto result = cast(immutable(T[U])) array;
    array = null;
    return result;
}

// @@@BUG@@@
version(none) unittest
{
    int[string] arr = ["a":1];
    auto arr1 = assumeUnique(arr);
    assert(is(typeof(arr1) == immutable(int[string])) && arr == null);
}

/**
 * Wraps a possibly-throwing expression in a $(D nothrow) wrapper so that it
 * can be called by a $(D nothrow) function.
 *
 * This wrapper function documents commitment on the part of the caller that
 * the appropriate steps have been taken to avoid whatever conditions may
 * trigger an exception during the evaluation of $(D expr).  If it turns out
 * that the expression $(I does) throw at runtime, the wrapper will throw an
 * $(D AssertError).
 *
 * (Note that $(D Throwable) objects such as $(D AssertError) that do not
 * subclass $(D Exception) may be thrown even from $(D nothrow) functions,
 * since they are considered to be serious runtime problems that cannot be
 * recovered from.)
 *
 * Params:
 *  expr = The expression asserted not to throw.
 *  msg = The message to include in the `AssertError` if the assumption turns
 *      out to be false.
 *  file = The source file name of the caller.
 *  line = The line number of the caller.
 *
 * Returns:
 *  The value of `expr`, if any.
 */
T assumeWontThrow(T)(lazy T expr,
                     string msg = null,
                     string file = __FILE__,
                     size_t line = __LINE__) nothrow
{
    import core.exception : AssertError;
    try
    {
        return expr;
    }
    catch(Exception e)
    {
        import std.range.primitives : empty;
        immutable tail = msg.empty ? "." : ": " ~ msg;
        throw new AssertError("assumeWontThrow failed: Expression did throw" ~
                              tail, file, line);
    }
}

///
unittest
{
    import std.math : sqrt;

    // This function may throw.
    int squareRoot(int x)
    {
        if (x < 0)
            throw new Exception("Tried to take root of negative number");
        return cast(int)sqrt(cast(double)x);
    }

    // This function never throws.
    int computeLength(int x, int y) nothrow
    {
        // Since x*x + y*y is always positive, we can safely assume squareRoot
        // won't throw, and use it to implement this nothrow function. If it
        // does throw (e.g., if x*x + y*y overflows a 32-bit value), then the
        // program will terminate.
        return assumeWontThrow(squareRoot(x*x + y*y));
    }

    assert(computeLength(3, 4) == 5);
}

unittest
{
    import core.exception : AssertError;

    void alwaysThrows()
    {
        throw new Exception("I threw up");
    }
    void bad() nothrow
    {
        assumeWontThrow(alwaysThrows());
    }
    assertThrown!AssertError(bad());
}

/**
Checks whether a given source object contains pointers or references to a given
target object.

Params:
    source = The source object
    target = The target object

Returns: $(D true) if $(D source)'s representation embeds a pointer
that points to $(D target)'s representation or somewhere inside
it.

If $(D source) is or contains a dynamic array, then, then these functions will check
if there is overlap between the dynamic array and $(D target)'s representation.

If $(D source) is a class, then it will be handled as a pointer.

If $(D target) is a pointer, a dynamic array or a class, then these functions will only
check if $(D source) points to $(D target), $(I not) what $(D target) references.

If $(D source) is or contains a union, then there may be either false positives or
false negatives:

$(D doesPointTo) will return $(D true) if it is absolutely certain
$(D source) points to $(D target). It may produce false negatives, but never
false positives. This function should be prefered when trying to validate
input data.

$(D mayPointTo) will return $(D false) if it is absolutely certain
$(D source) does not point to $(D target). It may produce false positives, but never
false negatives. This function should be prefered for defensively choosing a
code path.

Note: Evaluating $(D doesPointTo(x, x)) checks whether $(D x) has
internal pointers. This should only be done as an assertive test,
as the language is free to assume objects don't have internal pointers
(TDPL 7.1.3.5).
*/
bool doesPointTo(S, T, Tdummy=void)(auto ref const S source, ref const T target) @trusted pure nothrow
    if (__traits(isRef, source) || isDynamicArray!S ||
        isPointer!S || is(S == class))
{
    static if (isPointer!S || is(S == class) || is(S == interface))
    {
        const m = *cast(void**) &source;
        const b = cast(void*) &target;
        const e = b + target.sizeof;
        return b <= m && m < e;
    }
    else static if (is(S == struct) || is(S == union))
    {
        foreach (i, Subobj; typeof(source.tupleof))
            static if (!isUnionAliased!(S, i))
                if (doesPointTo(source.tupleof[i], target)) return true;
        return false;
    }
    else static if (isStaticArray!S)
    {
        foreach (size_t i; 0 .. S.length)
            if (doesPointTo(source[i], target)) return true;
        return false;
    }
    else static if (isDynamicArray!S)
    {
        import std.array : overlap;
        return overlap(cast(void[])source, cast(void[])(&target)[0 .. 1]).length != 0;
    }
    else
    {
        return false;
    }
}

// for shared objects
/// ditto
bool doesPointTo(S, T)(auto ref const shared S source, ref const shared T target) @trusted pure nothrow
{
    return doesPointTo!(shared S, shared T, void)(source, target);
}

/// ditto
bool mayPointTo(S, T, Tdummy=void)(auto ref const S source, ref const T target) @trusted pure nothrow
    if (__traits(isRef, source) || isDynamicArray!S ||
        isPointer!S || is(S == class))
{
    static if (isPointer!S || is(S == class) || is(S == interface))
    {
        const m = *cast(void**) &source;
        const b = cast(void*) &target;
        const e = b + target.sizeof;
        return b <= m && m < e;
    }
    else static if (is(S == struct) || is(S == union))
    {
        foreach (i, Subobj; typeof(source.tupleof))
            if (mayPointTo(source.tupleof[i], target)) return true;
        return false;
    }
    else static if (isStaticArray!S)
    {
        foreach (size_t i; 0 .. S.length)
            if (mayPointTo(source[i], target)) return true;
        return false;
    }
    else static if (isDynamicArray!S)
    {
        import std.array : overlap;
        return overlap(cast(void[])source, cast(void[])(&target)[0 .. 1]).length != 0;
    }
    else
    {
        return false;
    }
}

// for shared objects
/// ditto
bool mayPointTo(S, T)(auto ref const shared S source, ref const shared T target) @trusted pure nothrow
{
    return mayPointTo!(shared S, shared T, void)(source, target);
}

/// Pointers
unittest
{
    int  i = 0;
    int* p = null;
    assert(!p.doesPointTo(i));
    p = &i;
    assert( p.doesPointTo(i));
}

/// Structs and Unions
unittest
{
    struct S
    {
        int v;
        int* p;
    }
    int i;
    auto s = S(0, &i);

    // structs and unions "own" their members
    // pointsTo will answer true if one of the members pointsTo.
    assert(!s.doesPointTo(s.v)); //s.v is just v member of s, so not pointed.
    assert( s.p.doesPointTo(i)); //i is pointed by s.p.
    assert( s  .doesPointTo(i)); //which means i is pointed by s itself.

    // Unions will behave exactly the same. Points to will check each "member"
    // individually, even if they share the same memory
}

/// Arrays (dynamic and static)
unittest
{
    int i;
    int[]  slice = [0, 1, 2, 3, 4];
    int[5] arr   = [0, 1, 2, 3, 4];
    int*[]  slicep = [&i];
    int*[1] arrp   = [&i];

    // A slice points to all of its members:
    assert( slice.doesPointTo(slice[3]));
    assert(!slice[0 .. 2].doesPointTo(slice[3])); // Object 3 is outside of the
                                                  // slice [0 .. 2]

    // Note that a slice will not take into account what its members point to.
    assert( slicep[0].doesPointTo(i));
    assert(!slicep   .doesPointTo(i));

    // static arrays are objects that own their members, just like structs:
    assert(!arr.doesPointTo(arr[0])); // arr[0] is just a member of arr, so not
                                      // pointed.
    assert( arrp[0].doesPointTo(i));  // i is pointed by arrp[0].
    assert( arrp   .doesPointTo(i));  // which means i is pointed by arrp
                                      // itself.

    // Notice the difference between static and dynamic arrays:
    assert(!arr  .doesPointTo(arr[0]));
    assert( arr[].doesPointTo(arr[0]));
    assert( arrp  .doesPointTo(i));
    assert(!arrp[].doesPointTo(i));
}

/// Classes
unittest
{
    class C
    {
        this(int* p){this.p = p;}
        int* p;
    }
    int i;
    C a = new C(&i);
    C b = a;

    // Classes are a bit particular, as they are treated like simple pointers
    // to a class payload.
    assert( a.p.doesPointTo(i)); // a.p points to i.
    assert(!a  .doesPointTo(i)); // Yet a itself does not point i.

    //To check the class payload itself, iterate on its members:
    ()
    {
        foreach (index, _; Fields!C)
            if (doesPointTo(a.tupleof[index], i))
                return;
        assert(0);
    }();

    // To check if a class points a specific payload, a direct memmory check
    // can be done:
    auto aLoc = cast(ubyte[__traits(classInstanceSize, C)]*) a;
    assert(b.doesPointTo(*aLoc)); // b points to where a is pointing
}

unittest
{
    struct S1 { int a; S1 * b; }
    S1 a1;
    S1 * p = &a1;
    assert(doesPointTo(p, a1));

    S1 a2;
    a2.b = &a1;
    assert(doesPointTo(a2, a1));

    struct S3 { int[10] a; }
    S3 a3;
    auto a4 = a3.a[2 .. 3];
    assert(doesPointTo(a4, a3));

    auto a5 = new double[4];
    auto a6 = a5[1 .. 2];
    assert(!doesPointTo(a5, a6));

    auto a7 = new double[3];
    auto a8 = new double[][1];
    a8[0] = a7;
    assert(!doesPointTo(a8[0], a8[0]));

    // don't invoke postblit on subobjects
    {
        static struct NoCopy { this(this) { assert(0); } }
        static struct Holder { NoCopy a, b, c; }
        Holder h;
        cast(void)doesPointTo(h, h);
    }

    shared S3 sh3;
    shared sh3sub = sh3.a[];
    assert(doesPointTo(sh3sub, sh3));

    int[] darr = [1, 2, 3, 4];

    //dynamic arrays don't point to each other, or slices of themselves
    assert(!doesPointTo(darr, darr));
    assert(!doesPointTo(darr[0 .. 1], darr));

    //But they do point their elements
    foreach (i; 0 .. 4)
        assert(doesPointTo(darr, darr[i]));
    assert(doesPointTo(darr[0..3], darr[2]));
    assert(!doesPointTo(darr[0..3], darr[3]));
}

unittest
{
    //tests with static arrays
    //Static arrays themselves are just objects, and don't really *point* to anything.
    //They aggregate their contents, much the same way a structure aggregates its attributes.
    //*However* The elements inside the static array may themselves point to stuff.

    //Standard array
    int[2] k;
    assert(!doesPointTo(k, k)); //an array doesn't point to itself
    //Technically, k doesn't point its elements, although it does alias them
    assert(!doesPointTo(k, k[0]));
    assert(!doesPointTo(k, k[1]));
    //But an extracted slice will point to the same array.
    assert(doesPointTo(k[], k));
    assert(doesPointTo(k[], k[1]));

    //An array of pointers
    int*[2] pp;
    int a;
    int b;
    pp[0] = &a;
    assert( doesPointTo(pp, a));  //The array contains a pointer to a
    assert(!doesPointTo(pp, b));  //The array does NOT contain a pointer to b
    assert(!doesPointTo(pp, pp)); //The array does not point itslef

    //A struct containing a static array of pointers
    static struct S
    {
        int*[2] p;
    }
    S s;
    s.p[0] = &a;
    assert( doesPointTo(s, a)); //The struct contains an array that points a
    assert(!doesPointTo(s, b)); //But doesn't point b
    assert(!doesPointTo(s, s)); //The struct doesn't actually point itslef.

    //An array containing structs that have pointers
    static struct SS
    {
        int* p;
    }
    SS[2] ss = [SS(&a), SS(null)];
    assert( doesPointTo(ss, a));  //The array contains a struct that points to a
    assert(!doesPointTo(ss, b));  //The array doesn't contains a struct that points to b
    assert(!doesPointTo(ss, ss)); //The array doesn't point itself.
}


unittest //Unions
{
    int i;
    union U //Named union
    {
        size_t asInt = 0;
        int*   asPointer;
    }
    struct S
    {
        union //Anonymous union
        {
            size_t asInt = 0;
            int*   asPointer;
        }
    }

    U u;
    S s;
    assert(!doesPointTo(u, i));
    assert(!doesPointTo(s, i));
    assert(!mayPointTo(u, i));
    assert(!mayPointTo(s, i));

    u.asPointer = &i;
    s.asPointer = &i;
    assert(!doesPointTo(u, i));
    assert(!doesPointTo(s, i));
    assert( mayPointTo(u, i));
    assert( mayPointTo(s, i));

    u.asInt = cast(size_t)&i;
    s.asInt = cast(size_t)&i;
    assert(!doesPointTo(u, i));
    assert(!doesPointTo(s, i));
    assert( mayPointTo(u, i));
    assert( mayPointTo(s, i));
}

unittest //Classes
{
    int i;
    static class A
    {
        int* p;
    }
    A a = new A, b = a;
    assert(!doesPointTo(a, b)); //a does not point to b
    a.p = &i;
    assert(!doesPointTo(a, i)); //a does not point to i
}
unittest //alias this test
{
    static int i;
    static int j;
    struct S
    {
        int* p;
        @property int* foo(){return &i;}
        alias foo this;
    }
    assert(is(S : int*));
    S s = S(&j);
    assert(!doesPointTo(s, i));
    assert( doesPointTo(s, j));
    assert( doesPointTo(cast(int*)s, i));
    assert(!doesPointTo(cast(int*)s, j));
}
unittest //more alias this opCast
{
    void* p;
    class A
    {
        void* opCast(T)() if (is(T == void*))
        {
            return p;
        }
        alias foo = opCast!(void*);
        alias foo this;
    }
    assert(!doesPointTo(A.init, p));
    assert(!mayPointTo(A.init, p));
}

// Explicitly undocumented. It will be removed in May 2016. @@@DEPRECATED_2016-05@@@
deprecated ("pointsTo is ambiguous. Please use either of doesPointTo or mayPointTo")
alias pointsTo = doesPointTo;

/+
Returns true if the field at index $(D i) in ($D T) shares its address with another field.

Note: This does not merelly check if the field is a member of an union, but also that
it is not a single child.
+/
package enum isUnionAliased(T, size_t i) = isUnionAliasedImpl!T(T.tupleof[i].offsetof);
private bool isUnionAliasedImpl(T)(size_t offset)
{
    int count = 0;
    foreach (i, U; typeof(T.tupleof))
        if (T.tupleof[i].offsetof == offset)
            ++count;
    return count >= 2;
}
//
unittest
{
    static struct S
    {
        int a0; //Not aliased
        union
        {
            int a1; //Not aliased
        }
        union
        {
            int a2; //Aliased
            int a3; //Aliased
        }
        union A4
        {
            int b0; //Not aliased
        }
        A4 a4;
        union A5
        {
            int b0; //Aliased
            int b1; //Aliased
        }
        A5 a5;
    }

    static assert(!isUnionAliased!(S, 0)); //a0;
    static assert(!isUnionAliased!(S, 1)); //a1;
    static assert( isUnionAliased!(S, 2)); //a2;
    static assert( isUnionAliased!(S, 3)); //a3;
    static assert(!isUnionAliased!(S, 4)); //a4;
        static assert(!isUnionAliased!(S.A4, 0)); //a4.b0;
    static assert(!isUnionAliased!(S, 5)); //a5;
        static assert( isUnionAliased!(S.A5, 0)); //a5.b0;
        static assert( isUnionAliased!(S.A5, 1)); //a5.b1;
}

/*********************
 * Thrown if errors that set $(D errno) occur.
 */
class ErrnoException : Exception
{
    final @property uint errno() { return _errno; } /// Operating system error code.
    private uint _errno;
    this(string msg, string file = null, size_t line = 0) @trusted
    {
        _errno = .errno;
        version (CRuntime_Glibc)
        {
            char[1024] buf = void;
            auto s = core.stdc.string.strerror_r(errno, buf.ptr, buf.length);
        }
        else
        {
            auto s = core.stdc.string.strerror(errno);
        }
        super(msg ~ " (" ~ s[0..s.strlen].idup ~ ")", file, line);
    }
}

/++
    ML-style functional exception handling. Runs the supplied expression and
    returns its result. If the expression throws a $(D Throwable), runs the
    supplied error handler instead and return its result. The error handler's
    type must be the same as the expression's type.

    Params:
        E            = The type of $(D Throwable)s to catch. Defaults to $(D Exception)
        T1           = The type of the expression.
        T2           = The return type of the error handler.
        expression   = The expression to run and return its result.
        errorHandler = The handler to run if the expression throwed.

    Returns:
        expression, if it does not throw. Otherwise, returns the result of
        errorHandler.

    Example:
    --------------------
    //Revert to a default value upon an error:
    assert("x".to!int().ifThrown(0) == 0);
    --------------------

    You can also chain multiple calls to ifThrown, each capturing errors from the
    entire preceding expression.

    Example:
    --------------------
    //Chaining multiple calls to ifThrown to attempt multiple things in a row:
    string s="true";
    assert(s.to!int().
            ifThrown(cast(int)s.to!double()).
            ifThrown(cast(int)s.to!bool())
            == 1);

    //Respond differently to different types of errors
    assert(enforce("x".to!int() < 1).to!string()
            .ifThrown!ConvException("not a number")
            .ifThrown!Exception("number too small")
            == "not a number");
    --------------------

    The expression and the errorHandler must have a common type they can both
    be implicitly casted to, and that type will be the type of the compound
    expression.

    Example:
    --------------------
    //null and new Object have a common type(Object).
    static assert(is(typeof(null.ifThrown(new Object())) == Object));
    static assert(is(typeof((new Object()).ifThrown(null)) == Object));

    //1 and new Object do not have a common type.
    static assert(!__traits(compiles, 1.ifThrown(new Object())));
    static assert(!__traits(compiles, (new Object()).ifThrown(1)));
    --------------------

    If you need to use the actual thrown exception, you can use a delegate.
    Example:
    --------------------
    //Use a lambda to get the thrown object.
    assert("%s".format().ifThrown!Exception(e => e.classinfo.name) == "std.format.FormatException");
    --------------------
    +/
//lazy version
CommonType!(T1, T2) ifThrown(E : Throwable = Exception, T1, T2)(lazy scope T1 expression, lazy scope T2 errorHandler)
{
    static assert(!is(typeof(return) == void),
            "The error handler's return value(" ~ T2.stringof ~ ") does not have a common type with the expression(" ~ T1.stringof ~ ").");
    try
    {
        return expression();
    }
    catch(E)
    {
        return errorHandler();
    }
}

///ditto
//delegate version
CommonType!(T1, T2) ifThrown(E : Throwable, T1, T2)(lazy scope T1 expression, scope T2 delegate(E) errorHandler)
{
    static assert(!is(typeof(return) == void),
            "The error handler's return value(" ~ T2.stringof ~ ") does not have a common type with the expression(" ~ T1.stringof ~ ").");
    try
    {
        return expression();
    }
    catch(E e)
    {
        return errorHandler(e);
    }
}

///ditto
//delegate version, general overload to catch any Exception
CommonType!(T1, T2) ifThrown(T1, T2)(lazy scope T1 expression, scope T2 delegate(Exception) errorHandler)
{
    static assert(!is(typeof(return) == void),
            "The error handler's return value(" ~ T2.stringof ~ ") does not have a common type with the expression(" ~ T1.stringof ~ ").");
    try
    {
        return expression();
    }
    catch(Exception e)
    {
        return errorHandler(e);
    }
}

//Verify Examples
unittest
{
    import std.string;
    import std.conv;
    //Revert to a default value upon an error:
    assert("x".to!int().ifThrown(0) == 0);

    //Chaining multiple calls to ifThrown to attempt multiple things in a row:
    string s="true";
    assert(s.to!int().
            ifThrown(cast(int)s.to!double()).
            ifThrown(cast(int)s.to!bool())
            == 1);

    //Respond differently to different types of errors
    assert(enforce("x".to!int() < 1).to!string()
            .ifThrown!ConvException("not a number")
            .ifThrown!Exception("number too small")
            == "not a number");

    //null and new Object have a common type(Object).
    static assert(is(typeof(null.ifThrown(new Object())) == Object));
    static assert(is(typeof((new Object()).ifThrown(null)) == Object));

    //1 and new Object do not have a common type.
    static assert(!__traits(compiles, 1.ifThrown(new Object())));
    static assert(!__traits(compiles, (new Object()).ifThrown(1)));

    //Use a lambda to get the thrown object.
    assert("%s".format().ifThrown(e => e.classinfo.name) == "std.format.FormatException");
}

unittest
{
    import std.string;
    import std.conv;
    import core.exception;
    //Basic behaviour - all versions.
    assert("1".to!int().ifThrown(0) == 1);
    assert("x".to!int().ifThrown(0) == 0);
    assert("1".to!int().ifThrown!ConvException(0) == 1);
    assert("x".to!int().ifThrown!ConvException(0) == 0);
    assert("1".to!int().ifThrown(e=>0) == 1);
    assert("x".to!int().ifThrown(e=>0) == 0);
    static if (__traits(compiles, 0.ifThrown!Exception(e => 0))) //This will only work with a fix that was not yet pulled
    {
        assert("1".to!int().ifThrown!ConvException(e=>0) == 1);
        assert("x".to!int().ifThrown!ConvException(e=>0) == 0);
    }

    //Exceptions other than stated not caught.
    assert("x".to!int().ifThrown!StringException(0).collectException!ConvException() !is null);
    static if (__traits(compiles, 0.ifThrown!Exception(e => 0))) //This will only work with a fix that was not yet pulled
    {
        assert("x".to!int().ifThrown!StringException(e=>0).collectException!ConvException() !is null);
    }

    //Default does not include errors.
    int throwRangeError() { throw new RangeError; }
    assert(throwRangeError().ifThrown(0).collectException!RangeError() !is null);
    assert(throwRangeError().ifThrown(e=>0).collectException!RangeError() !is null);

    //Incompatible types are not accepted.
    static assert(!__traits(compiles, 1.ifThrown(new Object())));
    static assert(!__traits(compiles, (new Object()).ifThrown(1)));
    static assert(!__traits(compiles, 1.ifThrown(e=>new Object())));
    static assert(!__traits(compiles, (new Object()).ifThrown(e=>1)));
}

version(unittest) package
@property void assertCTFEable(alias dg)()
{
    static assert({ cast(void)dg(); return true; }());
    cast(void)dg();
}

/** This $(D enum) is used to select the primitives of the range to handle by the
  $(LREF handle) range wrapper. The values of the $(D enum) can be $(D OR)'d to
  select multiple primitives to be handled.

  $(D RangePrimitive.access) is a shortcut for the access primitives; $(D front),
  $(D back) and $(D opIndex).

  $(D RangePrimitive.pop) is a shortcut for the mutating primitives;
  $(D popFront) and $(D popBack).
 */
enum RangePrimitive
{
    front    = 0b00_0000_0001, ///
    back     = 0b00_0000_0010, /// Ditto
    popFront = 0b00_0000_0100, /// Ditto
    popBack  = 0b00_0000_1000, /// Ditto
    empty    = 0b00_0001_0000, /// Ditto
    save     = 0b00_0010_0000, /// Ditto
    length   = 0b00_0100_0000, /// Ditto
    opDollar = 0b00_1000_0000, /// Ditto
    opIndex  = 0b01_0000_0000, /// Ditto
    opSlice  = 0b10_0000_0000, /// Ditto
    access   = front | back | opIndex, /// Ditto
    pop      = popFront | popBack, /// Ditto
}

/** Handle exceptions thrown from range primitives.

Use the $(LREF RangePrimitive) enum to specify which primitives to _handle.
Multiple range primitives can be handled at once by using the $(D OR) operator
or the pseudo-primitives $(D RangePrimitive.access) and $(D RangePrimitive.pop).
All handled primitives must have return types or values compatible with the
user-supplied handler.

Params:
    E = The type of $(D Throwable) to _handle.
    primitivesToHandle = Set of range primitives to _handle.
    handler = The callable that is called when a handled primitive throws a
    $(D Throwable) of type $(D E). The handler must accept arguments of
    the form $(D E, ref IRange) and its return value is used as the primitive's
    return value whenever $(D E) is thrown. For $(D opIndex), the handler can
    optionally recieve a third argument; the index that caused the exception.
    input = The range to _handle.

Returns: A wrapper $(D struct) that preserves the range interface of $(D input).

opSlice:
Infinite ranges with slicing support must return an instance of
$(XREF range, Take) when sliced with a specific lower and upper
bound (see $(XREF_PACK range,primitives,hasSlicing)); $(D handle) deals with
this by $(D take)ing 0 from the return value of the handler function and
returning that when an exception is caught.
*/
auto handle(E : Throwable, RangePrimitive primitivesToHandle, alias handler, Range)(Range input)
    if (isInputRange!Range)
{
    static struct Handler
    {
        private Range range;

        static if (isForwardRange!Range)
        {
            @property typeof(this) save()
            {
                static if (primitivesToHandle & RangePrimitive.save)
                {
                    try
                    {
                        return typeof(this)(range.save);
                    }
                    catch(E exception)
                    {
                        return typeof(this)(handler(exception, this.range));
                    }
                }
                else
                    return typeof(this)(range.save);
            }
        }

        static if (isInfinite!Range)
        {
            enum bool empty = false;
        }
        else
        {
            @property bool empty()
            {
                static if (primitivesToHandle & RangePrimitive.empty)
                {
                    try
                    {
                        return this.range.empty;
                    }
                    catch(E exception)
                    {
                        return handler(exception, this.range);
                    }
                }
                else
                    return this.range.empty;
            }
        }

        @property auto ref front()
        {
            static if (primitivesToHandle & RangePrimitive.front)
            {
                try
                {
                    return this.range.front;
                }
                catch(E exception)
                {
                    return handler(exception, this.range);
                }
            }
            else
                return this.range.front;
        }

        void popFront()
        {
            static if (primitivesToHandle & RangePrimitive.popFront)
            {
                try
                {
                    this.range.popFront();
                }
                catch(E exception)
                {
                    handler(exception, this.range);
                }
            }
            else
                this.range.popFront();
        }

        static if (isBidirectionalRange!Range)
        {
            @property auto ref back()
            {
                static if (primitivesToHandle & RangePrimitive.back)
                {
                    try
                    {
                        return this.range.back;
                    }
                    catch(E exception)
                    {
                        return handler(exception, this.range);
                    }
                }
                else
                    return this.range.back;
            }

            void popBack()
            {
                static if (primitivesToHandle & RangePrimitive.popBack)
                {
                    try
                    {
                        this.range.popBack();
                    }
                    catch(E exception)
                    {
                        handler(exception, this.range);
                    }
                }
                else
                    this.range.popBack();
            }
        }

        static if (isRandomAccessRange!Range)
        {
            auto ref opIndex(size_t index)
            {
                static if (primitivesToHandle & RangePrimitive.opIndex)
                {
                    try
                    {
                        return this.range[index];
                    }
                    catch(E exception)
                    {
                        static if (__traits(compiles, handler(exception, this.range, index)))
                            return handler(exception, this.range, index);
                        else
                            return handler(exception, this.range);
                    }
                }
                else
                    return this.range[index];
            }
        }

        static if (hasLength!Range)
        {
            @property auto length()
            {
                static if (primitivesToHandle & RangePrimitive.length)
                {
                    try
                    {
                        return this.range.length;
                    }
                    catch(E exception)
                    {
                        return handler(exception, this.range);
                    }
                }
                else
                    return this.range.length;
            }
        }

        static if (hasSlicing!Range)
        {
            static if (hasLength!Range)
            {
                typeof(this) opSlice(size_t lower, size_t upper)
                {
                    static if (primitivesToHandle & RangePrimitive.opSlice)
                    {
                        try
                        {
                            return typeof(this)(this.range[lower .. upper]);
                        }
                        catch(E exception)
                        {
                            return typeof(this)(handler(exception, this.range));
                        }
                    }
                    else
                        return typeof(this)(this.range[lower .. upper]);
                }
            }
            else static if (is(typeof(Range.init[size_t.init .. $])))
            {
                static struct DollarToken {}
                enum opDollar = DollarToken.init;

                typeof(this) opSlice(size_t lower, DollarToken)
                {
                    static if (primitivesToHandle & RangePrimitive.opSlice)
                    {
                        try
                        {
                            return typeof(this)(this.range[lower .. $]);
                        }
                        catch(E exception)
                        {
                            return typeof(this)(handler(exception, this.range));
                        }
                    }
                    else
                        return typeof(this)(this.range[lower .. $]);
                }

                Take!Handler opSlice(size_t lower, size_t upper)
                {
                    static if (primitivesToHandle & RangePrimitive.opSlice)
                    {
                        try
                        {
                            return takeExactly(typeof(this)(this.range[lower .. $]), upper - 1);
                        }
                        catch(E exception)
                        {
                            return takeExactly(typeof(this)(handler(exception, this.range)), 0);
                        }
                    }
                    else
                        return takeExactly(typeof(this)(this.range[lower .. $]), upper - 1);
                }
            }
        }
    }

    return Handler(input);
}

///
pure @safe unittest
{
    import std.algorithm : equal, map, splitter;
    import std.conv : to, ConvException;

    auto s = "12,1337z32,54,2,7,9,1z,6,8";

    // The next line composition will throw when iterated
    // as some elements of the input do not convert to integer
    auto r = s.splitter(',').map!(a => to!int(a));

    // Substitute 0 for cases of ConvException
    auto h = r.handle!(ConvException, RangePrimitive.front, (e, r) => 0);
    assert(h.equal([12, 0, 54, 2, 7, 9, 0, 6, 8]));
}

///
pure @safe unittest
{
    import std.algorithm : equal;
    import std.range : retro;
    import std.utf : UTFException;

    auto str = "hello\xFFworld"; // 0xFF is an invalid UTF-8 code unit

    auto handled = str.handle!(UTFException, RangePrimitive.access,
            (e, r) => ' '); // Replace invalid code points with spaces

    assert(handled.equal("hello world")); // `front` is handled,
    assert(handled.retro.equal("dlrow olleh")); // as well as `back`
}

pure nothrow @safe unittest
{
    static struct ThrowingRange
    {
        pure @safe:
        @property bool empty()
        {
            throw new Exception("empty has thrown");
        }

        @property int front()
        {
            throw new Exception("front has thrown");
        }

        @property int back()
        {
            throw new Exception("back has thrown");
        }

        void popFront()
        {
            throw new Exception("popFront has thrown");
        }

        void popBack()
        {
            throw new Exception("popBack has thrown");
        }

        int opIndex(size_t)
        {
            throw new Exception("opIndex has thrown");
        }

        ThrowingRange opSlice(size_t, size_t)
        {
            throw new Exception("opSlice has thrown");
        }

        @property size_t length()
        {
            throw new Exception("length has thrown");
        }

        alias opDollar = length;

        @property ThrowingRange save()
        {
            throw new Exception("save has thrown");
        }
    }

    static assert(isInputRange!ThrowingRange);
    static assert(isForwardRange!ThrowingRange);
    static assert(isBidirectionalRange!ThrowingRange);
    static assert(hasSlicing!ThrowingRange);
    static assert(hasLength!ThrowingRange);

    auto f = ThrowingRange();
    auto fb = f.handle!(Exception, RangePrimitive.front | RangePrimitive.back,
            (e, r) => -1)();
    assert(fb.front == -1);
    assert(fb.back == -1);
    assertThrown(fb.popFront());
    assertThrown(fb.popBack());
    assertThrown(fb.empty);
    assertThrown(fb.save);
    assertThrown(fb[0]);

    auto accessRange = f.handle!(Exception, RangePrimitive.access,
            (e, r) => -1);
    assert(accessRange.front == -1);
    assert(accessRange.back == -1);
    assert(accessRange[0] == -1);
    assertThrown(accessRange.popFront());
    assertThrown(accessRange.popBack());

    auto pfb = f.handle!(Exception, RangePrimitive.pop, (e, r) => -1)();

    pfb.popFront(); // this would throw otherwise
    pfb.popBack(); // this would throw otherwise

    auto em = f.handle!(Exception,
            RangePrimitive.empty, (e, r) => false)();

    assert(!em.empty);

    auto arr = f.handle!(Exception,
            RangePrimitive.opIndex, (e, r) => 1337)();

    assert(arr[0] == 1337);

    auto arr2 = f.handle!(Exception,
            RangePrimitive.opIndex, (e, r, i) => i)();

    assert(arr2[0] == 0);
    assert(arr2[1337] == 1337);

    auto save = f.handle!(Exception,
        RangePrimitive.save,
        function(Exception e, ref ThrowingRange r) {
            return ThrowingRange();
        })();

    save.save;

    auto slice = f.handle!(Exception,
        RangePrimitive.opSlice, (e, r) => ThrowingRange())();

    auto sliced = slice[0 .. 1337]; // this would throw otherwise

    static struct Infinite
    {
        pure @safe:
        enum bool empty = false;
        int front() { assert(false); }
        void popFront() { assert(false); }
        Infinite save() @property { assert(false); }
        static struct DollarToken {}
        enum opDollar = DollarToken.init;
        Take!Infinite opSlice(size_t, size_t) { assert(false); }
        Infinite opSlice(size_t, DollarToken)
        {
            throw new Exception("opSlice has thrown");
        }
    }

    static assert(isInputRange!Infinite);
    static assert(isInfinite!Infinite);
    static assert(hasSlicing!Infinite);

    assertThrown(Infinite()[0 .. $]);

    auto infinite = Infinite.init.handle!(Exception,
        RangePrimitive.opSlice, (e, r) => Infinite())();

    auto infSlice = infinite[0 .. $]; // this would throw otherwise
}
