[Issue 6573] New: Add isOneOf to std.traits

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=6573

           Summary: Add isOneOf to std.traits
           Product: D
           Version: D2
          Platform: Other
        OS/Version: Windows
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: Phobos
        AssignedTo: nobody at puremagic.com
        ReportedBy: andrej.mitrovich at gmail.com


--- Comment #0 from Andrej Mitrovic <andrej.mitrovich at gmail.com> 2011-08-29 19:15:23 PDT ---
I think Steven Schveighoffer came up with this originally:

template isOneOf(X, T...)
{
    static if (!T.length)
        enum bool isOneOf = false;
    else static if (is (X == T[0]))
        enum bool isOneOf = true;
    else
        enum bool isOneOf = isOneOf!(X, T[1..$]);
}

It's very useful as a replacement for multiple checks on a single type
parameter, e.g.:

void foo(T)(T t) if (is(T == Type1) || is(T == Type2) || is(T == Type3))

turns into:

void foo(T)(T t) if (isOneOf!(T, Type1, Type2, Type3))

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