Blog post: What D got wrong

[Steven Schveighoffer]

On 12/19/18 2:58 PM, Neia Neutuladh wrote:
> On Wed, 19 Dec 2018 17:28:01 +0000, Vijay Nayar wrote:
>> Could you please elaborate a little bit more on this?  In the linked
>> program, I had expected that "ref" would return a reference to "a" that
>> would behave similar to a pointer.
> 
> They work like pointers that automatically dereference when assigning to
> the base type.
> 
> Only three things in D can be ref:
> * A function parameter
> * A function return value
> * A foreach variable (since that's either going to be a function return
> value, a function parameter, or a pointer, depending on what you're
> iterating over)
> 
> So when the compiler sees something like:
> 
>      ref int foo();
>      auto a = foo();
> 
> It sees that the type of 'a' has to be the same as the return type of
> 'foo'. Except that's not possible, so it uses the nearest equivalent type:
> int.

I would say it a little bit differently -- the return *type* of foo is 
int. In D, ref is not part of the type at all.

For example, even when it *could* use ref, it doesn't:

int x;
ref int foo() { return x; }

void bar(Args...)(Args args)
{
    pragma(msg, __traits(isRef, args[0]));
}

bar(foo()); // outputs false at compile time

The storage class is completely separate from the type. Which is 
different from C++, where it's like a storage class but is really a type 
constructor, hence Walter's post.

-Steve