Why does D not have generics?

[Ola Fosheim Grøstad]

On Tuesday, 12 January 2021 at 21:32:46 UTC, Ola Fosheim Grøstad 
wrote:
> 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;
> }

An improvement is to define a helper function:

auto as_stack(T)(T* obj){
     auto stack = obj.as_StackConcept();
     static assert (is_StackConcept!(typeof(stack)));
     return stack;
}


Then you can just do:

auto pop_second(T)(T* obj){
     auto stack = obj.as_stack();
     auto tmp = stack.pop();
     auto tmp2 = stack.pop();
     stack.push(tmp);
     return tmp2;
}


Or:

auto pop_second(T)(T* obj){
     auto tmp =  obj.as_stack.pop();
     auto tmp2 =  obj.as_stack.pop();
     obj.as_stack.push(tmp);
     return tmp2;
}