opAssign and references

[Timon Gehr]

On 01/31/2012 03:03 PM, Nicolas Silva wrote:
> Hi,
>
> I'm playing with variants and I noticed that opAssign is not invoked
> when an assignation is done on a reference.
>
> here is the test case:
>
> import std.variant;
>
> struct Foo
> {
>      Variant a;
>      Variant b;
>      ref Variant refA()
>      {
>          return a;
>      }
> }
>
> void main()
> {
>      Foo f1;
>      f1.a = 42; // ok
>      f1.b = 23; // ok
>
>      f1.refA() = 24; // Error: cannot implicitly convert expression
> (24) of type int to VariantN!(maxSize)

Works for me. Which version of the compiler are you using?


>      f1.refA().opAssign( 24 ); // ok, but not very nice...
>
>      // slightly OT but
>      Foo f2 = { a: 10 }; // Error: cannot implicitly convert expression
> (10) of type int to VariantN!(maxSize)

This is http://d.puremagic.com/issues/show_bug.cgi?id=7019

> }
>
>
> Is it normal? Am I missing something?
> I took Variant as an example because it does use opAssign but one
> could create a struct defining opAssign with the same results.
>
> More generally, I feel like I don't really understand the semantic of
> opAssign (or maybe references). I'd intuitively expect it to be
> invoked when the "=" operator is used on a reference and I'd also
> expect it to be invoked in struct initializers (though there might be
> something  about compiletime / runtime stories in this particular
> case, yet i think one would expect it to just work).
>
> D aims at being simple and intuitive, and in this case it looks not so
> intuitive to me.

If something is not as simple and intuitive as it ought to be, there 
might be a compiler bug.

>
> Best regards,
>
> Nicolas Silva