A while back, we talked about how using std::span instead of C-style arrays makes your code safer and easier to reason about. std::span, added in C++20, is a non-owning view over a contiguous sequence of objects - think of it as a string_view, but for arrays. C++23 continued building on this foundation, bringing related utilities such as <spanstream> and mdspan, the multidimensional cousin of span. Now let’s see what additional improvements we are getting with C++26.

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C++26 introduces four targeted improvements to std::span. First, span<const T> can now be constructed from an initializer list, closing an ergonomic gap compared to string_view. Second, span gains a bounds-checked at() member function that throws std::out_of_range, bringing it in line with other standard containers. Third, span, mdspan, expected, out_ptr, and inout_ptr are added to the freestanding subset of the standard library (with at() excluded since it throws). Fourth, CTAD for both span and mdspan becomes integral_constant-aware, allowing the compiler to deduce static extents instead of always falling back to dynamic_extent.

C++26: Span improvements

P2447R6 : std::span over an initializer list

P2833R2 : Freestanding Library: inout expected span