[Issue 14544] New: isForwardRange failed to recognise valid forward range

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=14544

          Issue ID: 14544
           Summary: isForwardRange failed to recognise valid forward range
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: Phobos
          Assignee: nobody at puremagic.com
          Reporter: ketmar at ketmar.no-ip.org

this code fails static assertion:

struct Input {
  auto opSlice (size_t start, size_t end) {
    static struct InputSlice {
      @property bool empty () { return false; }
      @property char front () { return 0; }
      void popFront () {}
      InputSlice save () { return this; }
    }
    import std.range.primitives;
    static assert(isForwardRange!InputSlice);
    return InputSlice();
  }
}


fixing code like this tames `isForwardRange`:

template isForwardRange(R)
{
    enum bool isForwardRange = isInputRange!R && is(typeof(
    (inout int = 0)
    {
        R r1 = R.init;
        //old: static assert (is(typeof(r1.save) == R));
        auto s1 = r1.save;
        static assert (is(typeof(s1) == R));
    }));
}

i wonder if some other checking primitives has similar bug.

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