what are the rules for @nogc and @safe attributes inference?

[Neia Neutuladh]

On Fri, 30 Nov 2018 20:41:03 +0000, ikod wrote:
> I can't find the reason why nogc/nothrow can't be inferred in this case:
> 
> class S(K,V)
> {
>      auto get/*()*/(K a) {
>          return 0;
>      }
> }
> void main() @nogc nothrow {
>      S!(int, string) sia;
>      auto v = sia.get(1);
> }

class Nefarious : S!(int, string)
{
  override int get(int a)
  {
    // Whoops, I used the GC
    return new char[a].length;
  }
}

The compiler can't prove that a variable of type S!(int, string) will not 
be of type Nefarious, which uses the GC, so it can't infer @nogc for S.get.

However, if you make the function final, then the compiler can infer it to 
be pure nothrow @nogc @safe.

Or if you use a struct instead of a class, structs don't do inheritance, 
so the compiler can infer attributes without worrying about nefarious 
inheritance.

> But everything is ok if you uncomment parentheses after get.

Templated functions are implicitly final.