• 60rntogo (28/28) Sep 17 2020 I suspect that this is similar to the issue I asked about here:
• Simen =?UTF-8?B?S2rDpnLDpXM=?= (27/36) Sep 17 2020 Usually, that would be:
• 60rntogo (7/24) Sep 17 2020 Yes, I tried that. It didn't work so I assumed that it must have

60rntogo <60rntogo gmail.com> writes:

I suspect that this is similar to the issue I asked about here: 
https://forum.dlang.org/post/vukxaqprjbyrdpioukwa forum.dlang.org, but I can't
figure it out.

This compiles:

---
private mixin template assign(string op_)
{
   ref auto opOpAssign(string op, this RHS)(RHS rhs) if (op == op_)
   {
     mixin("x " ~ op ~ "= rhs.x;");
     return this;
   }
}

struct V
{
   int x;

   mixin assign!"+";
   // mixin assign!"-";
}

unittest
{
   auto v = V(2);
   v += v;
   assert(v.x == 4);
}
---

However, if I uncomment the second mixin, there is an error "v is 
not a scalar, it is a V". I guess I somehow need to merge these 
overloads, but I don't know how.

Simen =?UTF-8?B?S2rDpnLDpXM=?= <simen.kjaras gmail.com> writes:

On Thursday, 17 September 2020 at 21:05:59 UTC, 60rntogo wrote:
 struct V
 {
   int x;

   mixin assign!"+";
   // mixin assign!"-";
 }

 However, if I uncomment the second mixin, there is an error "v 
 is not a scalar, it is a V". I guess I somehow need to merge 
 these overloads, but I don't know how.

Usually, that would be:

struct V {
     int x;

     mixin assign!"+" a;
     mixin assign!"-" b;
     alias opOpAssign = a.opOpAssign;
     alias opOpAssign = b.opOpAssign;
}

However, I can't seem to get that working. It seems to be an 
instance of this issue:
https://issues.dlang.org/show_bug.cgi?id=18118

Note that explicitly calling the methods does work:

     v.opOpAssign!"-"(v);
     v.opOpAssign!"+"(v);


I don't know any good workarounds for this, you'll probably have 
to write a separate opOpAssign method for V that performs the 
forwarding to the mixed-in methods. This is, to put it very 
nicely, not an optimal solution.


btw, I'm somewhat surprised by your use of a template this 
parameter 
(https://dlang.org/spec/template.html#template_this_parameter). 
Generally this will work, but you're probably better off with

     ref auto opOpAssign(string op)(typeof(this) rhs) if (op == 
op_)


--
   Simen

60rntogo <60rntogo gmail.com> writes:

On Thursday, 17 September 2020 at 22:07:54 UTC, Simen Kjærås 
wrote:
 Usually, that would be:

 struct V {
     int x;

     mixin assign!"+" a;
     mixin assign!"-" b;
     alias opOpAssign = a.opOpAssign;
     alias opOpAssign = b.opOpAssign;
 }

 However, I can't seem to get that working. It seems to be an 
 instance of this issue:
 https://issues.dlang.org/show_bug.cgi?id=18118

Yes, I tried that. It didn't work so I assumed that it must have 
been wrong. Is this a bug in the compiler or an issue in the 
language specification?

 btw, I'm somewhat surprised by your use of a template this 
 parameter 
 (https://dlang.org/spec/template.html#template_this_parameter). 
 Generally this will work, but you're probably better off with

     ref auto opOpAssign(string op)(typeof(this) rhs) if (op == 
 op_)

I learned it from here: http://ddili.org/ders/d.en/mixin.html, 
could you elaborate on why this is not advisable?