No implicit opOpAssign for structs with basic types?

[Robert M. Münch]

On 2020-04-04 10:32:32 +0000, Ferhat Kurtulmuş said:

> struct S {
>      float a;
>      float b;
> 
>      S opOpAssign(string op)(ref S rhs) if (op == "+"){
>          this.a += rhs.a;
>          this.b += rhs.b;
>          return this;
>      }
> }

If the struct is from some 3rd party source, how can I add such an 
operator overloading to it? Is it possible to "extend" a struct later?

-- 
Robert M. Münch
http://www.saphirion.com
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