Re: another question on hidden mixin names

[60rntogo via Digitalmars-d-learn]

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?

Re: another question on hidden mixin names

[Simen Kjærås via Digitalmars-d-learn]

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

another question on hidden mixin names

[60rntogo via Digitalmars-d-learn]

I suspect that this is similar to the issue I asked about here: 
https://forum.dlang.org/post/vukxaqprjbyrdpiou...@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.