[Issue 15926] New: Peculiar behavior of 'inout'

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=15926

          Issue ID: 15926
           Summary: Peculiar behavior of 'inout'
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: bugzilla at digitalmars.com

Discussion:

http://www.digitalmars.com/d/archives/digitalmars/D/So_what_does_inout_int_0_do_283407.html

Use case:

https://github.com/D-Programming-Language/phobos/blob/master/std/range/primitives.d#L152

Given the code:

template isInputRange(R)
{
    enum bool isInputRange = is(typeof(
    (inout int = 0)
    {
        R r = R.init;     // can define a range object
        if (r.empty) {}   // can test for empty
        r.popFront();     // can invoke popFront()
        auto h = r.front; // can get the front of the range
    }));
}

///
@safe unittest
{
    struct A {}
    struct B
    {
        void popFront();
        @property bool empty();
        @property int front();
    }
    static assert(!isInputRange!A);
    static assert( isInputRange!B);
    static assert( isInputRange!(int[]));
    static assert( isInputRange!(char[]));
    static assert(!isInputRange!(char[4]));
    static assert( isInputRange!(inout(int)[]));
}

What is the 'inout int = 0' doing there and why does 'static assert(
isInputRange!(inout(int)[]));' fail when it is removed? There seems to be some
sort of undocumented behavior going on?

--