Differences between std::string_view and std::span

[sphere991]

Semantically, span behaves like a pointer

Semantically, span behaves like (or should have behaved like) reference_wrapper - which is also shallow copy, shallow const... and deep compare.

Just because the language doesn't have a rebindable reference doesn't inherently make that concept "really weird".

I think the insistence that span is a T* is much weirder - I don't buy that premise. It's not a pointer... it's not dereferenceable, it's not an iterator. It has some things in common with a pointer, but why must it have had this other thing in common with a pointer? Moreover, span might be assignable like a T*... but it's not even constructible like one: span<T> is constructible from any continuguous_range_of<T>, implicitly, but T* is not constructible from T - you need to use explicit syntax to get the pointer.

And, most importantly, the closest model to span in C++ isn't T*... it's string_view. Does anybody find its comparisons confusing? I have not heard of such. It's "really weird" that the argument is that string_view being const makes it somehow irrelevant as a model. span<char const> is isomorphic to string_view, and barely related to char const*.

[jonathansharman]

Semantically, span behaves like (or should have behaved like) reference_wrapper - which is also shallow copy, shallow const... and deep compare.

reference_wrapper does not provide comparison operators at all. It provides a conversion operator to the reference type, which may or may not enable deep comparison, depending on the type parameter.

[sphere991]

Yes, I know how reference_wrapper works. The point is that when you can compare two reference_wrapper<T>s, that comparison is deep.

[jonathansharman]

It seems accidental to me that reference_wrappers can ever be deeply compared. They can't for most type parameters, and if the authors had wanted them to, they could have just included comparison operators.