No, you misunderstand. The function doesn't return any type, it returns _a_ type. Types are values in Zig and returning them from function is how generics are implemented.
If you must return different types depending on the argument in D, it's also possible.
Here's a silly example:
struct ArrayList(T, alias capacity) {
private T[capacity] array;
private uint _length;
uint length() const => _length;
T get(uint index) const => array[index];
void add(T t) {
array[_length++] = t;
}
}
struct EmptyList(T) {
uint length() const => 0;
}
/// This will return a different type depending on the length argument,
/// which is like a Zig comptime argument.
/// We cannot return the type itself, but the result is very similar.
auto createArrayList(T, alias length)() {
static if (length == 0) {
return EmptyList!T();
} else {
return ArrayList!(T, length)();
}
}
void main()
{
import std.stdio;
auto empty = createArrayList!(int, 0);
writeln(empty);
auto list = createArrayList!(int, 2);
list.add(5);
list.add(6);
writeln(list);
}
EmptyList!int()
ArrayList!(int, 2)([5, 6], 2)Regardless, we are now very far removed from the original code I was commenting on, which doesn't use auto to return different types.