Fixed-size std::span vs std::array

Question

C++20 includes std::span, which "describes an object that can refer to a contiguous sequence of objects with the first element of the sequence at position zero". Its interface is very close to std::array, though it supports dynamic extent as well as fixed one.

The obvious difference is that std::array owns its elements (and so its destructor destroys them) and std::span doesn't.

Is there anything else array can be used for that span can't?

isnt span for a different use-case? I might be wrong, but I think span is like `string_view` for `string`s — 463035818_is_not_an_ai, Jun 05 '18 at 14:04
Span is for completely different reasons. Span is basically a safe idiom for C++ dynamic array - incapsulation of a pointer to begin and end of a sequence. — SergeyA, Jun 05 '18 at 14:06
`span` is to `array` what `string_view` it to `string`. `array` can be used to copy memory around while `span` only manipulates handles to it. — YSC, Jun 05 '18 at 14:22
"Is there anything an `int` can be used for that an `int*` cannot?" — Yakk - Adam Nevraumont, Jun 05 '18 at 14:24

score 19 · Accepted Answer · answered Jun 05 '18 at 14:27

span is to array as pointers are to values.

Is there anything an int can be used for than an int* cannot?

If you swept your code base and replaced every int with an int* you'd have a completely nonsense codebase, even if you added a * at every point-of-use of the int*. If you swept your code base and replaced every std::array with a std::span, the same would be true.

Pointers and values are different things. You can jump through hoops and try to deal with pointers as if they are the value of the thing they point to, but trying to do so is often difficult, and the result is often incoherent.

Fixed-size std::span vs std::array

1 Answers1