Why does D not have generics?

[Paul Backus]

On Tuesday, 12 January 2021 at 21:32:46 UTC, Ola Fosheim Grøstad 
wrote:
> So, this is one, perhaps clumsy way of doing it:
>
[...]
>
> auto pop_second(T)(T* obj){
>     auto stack = obj.as_StackConcept();
>     static assert (is_StackConcept!(typeof(stack)));
> 	auto tmp = stack.pop();
>     auto tmp2 = stack.pop();
>     stack.push(tmp);
>     return tmp2;
> }

You have written a generic function that accepts any type 
(unconstrained `T`), but fails to instantiate for most of them 
(e.g. `pop_second!int` would not compile). In a language like 
Rust or Java with type-checked generics, the compiler would 
reject this function definition.