From bug tracker I see that Proxy has a few issues, so this has likely been seen. But what would cause this error?

tmp/c.d(16): Error: overloads pure nothrow @safe double(auto ref CcRate b) and pure nothrow @safe double(auto ref CcRate b) both match argument list for opBinary

The error refers to two methods with the same signature. In typecons there are only two "Binary" methods, opBinary and opBinaryRight, both in Proxy, so where is the duplication/conflict coming from?

Thanks
Dan
---------------
import std.stdio;
import std.typecons;
import std.algorithm;

struct CcRate {
  private double rate = 0;
  mixin Proxy!rate;

  this(double rate) {
    this.rate = rate;
  }
}

unittest {
    CcRate r1 = 0.033, r2 = 0.002;
    writeln(r1+r2);  // compile error
}
---------------

On Thursday, 25 October 2012 at 16:39:57 UTC, Dan wrote:
> From bug tracker I see that Proxy has a few issues, so this has likely been seen. But what would cause this error?
>
> tmp/c.d(16): Error: overloads pure nothrow @safe double(auto ref CcRate b) and pure nothrow @safe double(auto ref CcRate b) both match argument list for opBinary
>
> The error refers to two methods with the same signature. In typecons there are only two "Binary" methods, opBinary and opBinaryRight, both in Proxy, so where is the duplication/conflict coming from?
>
> Thanks
> Dan
> ---------------
> import std.stdio;
> import std.typecons;
> import std.algorithm;
>
> struct CcRate {
>   private double rate = 0;
>   mixin Proxy!rate;
>
>   this(double rate) {
>     this.rate = rate;
>   }
> }
>
> unittest {
>     CcRate r1 = 0.033, r2 = 0.002;
>     writeln(r1+r2);  // compile error
> }
> ---------------

Still trying to understand this. I found that if I change the following in Proxy it this example (r1 + r2) works fine. Plus the unit tests that are there still work. But, honestly I don't understand why...yet.

Thanks,
Dan

----- From typecons.Proxy -----
    auto ref opBinary     (string op, this X, B)(auto ref B b) { return mixin("a "~op~" b"); }
----- To -----
    auto ref opBinary     (string op, this X, B)(auto ref B b) if(!is(X == B)) { return mixin("a "~op~" b"); }
-----

On Friday, 26 October 2012 at 15:14:56 UTC, Dan wrote:
> Still trying to understand this. I found that if I change the following in Proxy it this example (r1 + r2) works fine. Plus the unit tests that are there still work. But, honestly I don't understand why...yet.
>
> Thanks,
> Dan
>
> ----- From typecons.Proxy -----
>     auto ref opBinary     (string op, this X, B)(auto ref B b) { return mixin("a "~op~" b"); }
> ----- To -----
>     auto ref opBinary     (string op, this X, B)(auto ref B b) if(!is(X == B)) { return mixin("a "~op~" b"); }
> -----

From http://dlang.org/operatoroverloading.html, it is an error for both overloads of opBinary (opBinary and opBinaryRight) to match. Since the signatures for the two overloads in std.typecons are identical, this looks like a bug to me.

Your modified version works (far as I can see) because it excludes one of the overloads from being matched, allowing the other to be used (opBinaryRight).