[Issue 6197] New: std.traits.isImplicitlyConvertible returns some wrong results.

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=6197

           Summary: std.traits.isImplicitlyConvertible returns some wrong
                    results.
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Phobos
        AssignedTo: nobody at puremagic.com
        ReportedBy: k.hara.pg at gmail.com


--- Comment #0 from Kenji Hara <k.hara.pg at gmail.com> 2011-06-23 04:01:22 PDT ---
pragma(msg, implicitlyConverts!(const(uint), ubyte));
should print 'false', but 'true'.

Cause of this bug:

Current implementation is here:
template isImplicitlyConvertible(From, To)
{
    enum bool isImplicitlyConvertible = is(typeof({
                        void fun(To) {}
                        From v;
                        fun(f);
                    }()));
}

When From=const(uint) and To=ubyte, it is rewites as

    enum bool isImplicitlyConvertible = is(typeof({
                        void fun(ubyte) {}
                        const(uint) v;
                        fun(f);
                    }()));

and function argument v is *optimized* to its initial value 0u and matches to
parameter type ubyte by literal conversion.

How to fix:
The variables its initializers are not visible does not cause optimization.
So rewrite as:

    enum bool isImplicitlyConvertible = is(typeof({
                      void fun(ref From v){
                        void gun(To) {}
                        gun(v);
                      }
                    }()));

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