[Issue 15859] opApply resolution on attributes

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=15859

--- Comment #1 from qs.il.paperinik at gmail.com ---
(In reply to qs.il.paperinik from comment #0)
> struct X
> {
>     int opApply(int delegate(string) dg)
>     {
>         return dg("impure");
>     }
> 
>     int opApply(int delegate(string) pure dg) pure
>     {
>         return dg("pure");
>     }
> }
> 
> void main()
> {
>     X x;
>     string result;
>
>     [ ... ] 
>
>     /+ (1)
>     foreach (string s; x)
>     {
>         result = s;
>     }
>     writeln(result); // x.opApply matches more than one declaration
>     +/
>     /+ (2)
>     foreach (string s; x)
>     {
>         result = s;
>         write("");
>     }
>     writeln(result); // x.opApply matches more than one declaration
>     +/
> }

For (1) this is true to some extent. The constructed delegate is pure, but can
be matched to the non-pure version of opApply.
For (2) the compiler rejects valid because the delegate is impure and can only
match the impure opApply.

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