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digitalmars.D.learn - Template mixin + operator overloading question

reply Boyan Lazov <boyan.lazov gmail.com> writes:
Hello,

I seem to have a problem when I use a template mixin and then try 
to overload operators both in the mixin and in a struct from 
where it's instantiated.
So the idea is that I have a few operators defined in the mixin, 
then a few more in the struct, and I want to forward all 
operations not explicitly defined in the struct to the ones in 
the mixin (and I don't want to do alias this for a variety of 
unrelated reasons).

Basically the simplest code that gives me problems is:

import std.stdio;

mixin template Impl(T) {
     T v;
     int opBinary(string s: "+")(T other) {
         writeln("Single +");
         return 0;
     }
     int opBinary(string s: "+")(T[] other) {
         writeln("Array +");
         return 0;
     }
}

struct Pt {
     mixin Impl!float impl;

     int opBinary(string s: "*")(float other) {
         writeln("Single *");
         return 0;
     }

     int opBinary(string s, T)(T v) {
         //Pt already has opBinary defined, so the operators in 
the mixin not visible
         //Thought that delegating to the mixin should be done 
this way
         writeln("Delegate ", s);
         return impl.opBinary!(s)(v);
     }
}


void main() {
     Pt pt;
     int r = pt + [1f, 2f];
     writeln("R: ", r);
}

This results in an infinite loop though. Seems like 
Pt.opBinary!("+", float[]) is called over and over. Which is a 
bit un-intuitive to me - I'm not sure why calling 
impl.opBinary!(s) can result in endless recursion.

The problem appears only when I have 2 operators in the mixin 
that I try to forward to - e.g. the two overloads of "+" in this 
case. If I have just 1, it works ok, if I have none, the error 
message is helpful.

Any ideas what I'm doing wrong?
Thanks!
Oct 11 2019
parent reply Dennis <dkorpel gmail.com> writes:
On Friday, 11 October 2019 at 12:45:59 UTC, Boyan Lazov wrote:

 Any ideas what I'm doing wrong?


Nothing, it's a bug.
https://issues.dlang.org/show_bug.cgi?id=19476
Oct 11 2019
parent Boyan Lazov <boyan.lazov gmail.com> writes:
On Friday, 11 October 2019 at 13:13:46 UTC, Dennis wrote:

 On Friday, 11 October 2019 at 12:45:59 UTC, Boyan Lazov wrote:

 Any ideas what I'm doing wrong?


 Nothing, it's a bug.
 https://issues.dlang.org/show_bug.cgi?id=19476


Alright, I see
Well, the alias workaround works, so that seems just as good. 
Thanks!
Oct 11 2019