[Issue 11947] New: std.typecons.Proxy incorrectly handles variadic member templates

[d-bugmail at puremagic.com]

https://d.puremagic.com/issues/show_bug.cgi?id=11947

           Summary: std.typecons.Proxy incorrectly handles variadic member
                    templates
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Phobos
        AssignedTo: nobody at puremagic.com
        ReportedBy: stanislav.blinov at gmail.com


--- Comment #0 from Stanislav Blinov <stanislav.blinov at gmail.com> 2014-01-19 01:41:15 PST ---
When forwarding member function calls, Proxy incorrectly handles cases when
member template is variadic:

import std.typecons : Proxy;

struct RealThing {
    void variadic(T...)(T args) {}
}

struct Impostor {
    private RealThing p;
    mixin Proxy!p;
}

void main()
{
    Impostor test;
    test.variadic();        // ok
    test.variadic("hello"); // error instantiating
}


Proposed solution:



// Original (std.typecons at 3884):
// member template
template opDispatch(T...)
{
    auto ref opDispatch(this X, Args...)(auto ref Args args){ return
mixin("a."~name~"!T(args)"); }
}

// Change to (std.typecons at 3884):
// member template
template opDispatch(T...)
{
    auto ref opDispatch(this X, Args...)(auto ref Args args)
    { 
        // T is empty, deduction is in effect
        static if (Args.length) { return
mixin("a."~name~"!"~Args.stringof~"(args)"); } 
        // T is explicitly specified        
        else                    { return mixin("a."~name~"!T(args)");          
      }
    }
}

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