[Issue 12583] Allow user defined "retro" range

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=12583

--- Comment #4 from Jonathan M Davis <jmdavisProg at gmx.com> ---
If myRange.retro() fails, because typeof(myRange) defined retro(int) but not
retro, then that sounds like a bug with UFCS to me. retro(int) doesn't match
myRange.retro(), but std.range.retro does, so std.range.retro should be called
rather than the member function.

If a member function has a different signature than the free function, then
it's not intended as a replacement for the free function, and it shouldn't be
conflicting with the free function at all.

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