Differences between std::array and boost::array

Question

It is fully safe to change boost::array to std::array ? Can it cause any discrepancies?

Is boost::array better over std::array (performance?)?

Answer 1

std::array<T,N> and boost::array<T,N> are standard layout aggregates containing nothing but an array of T[N] .

Their interaction with namespace boost and namespace std may be different (Specifically, ADL will find std functions for std::array , and boost functions for boost::array ).

So, if there is a function foo in boost , calling foo(some_array) might work if some_array was from boost , and not if it was from std .

The only container algorithms currently in std are std::begin and std::end (and similar the new ones size empty etc if you include near-future ones). Ranges v3 (or whatever gets published) might add some more.

There are more container algorithms in boost than in std . Some of them might fail to build.

In the worst case, someone could write a function with the same name as a container algorithm in boost , with an argument that can implicitly convert from std::array , and the unqualified call to that function could result in a conversion after you change the variable type, while before it called the boost container algorithm.

Similarly, someone could write code that explicitly checks if a template argument is a boost::array and behave differently if it is.

Both of those are a bit of a stretch.

Finally, std::array has modern noexcept decoration, and boost has a public c_array member you can get at (the name std::array member variables is, I believe, not specified). (via @Potatoswatter). I'd personally expect std::array to have better support going forward, as boost::array mainly existed because std lacked the functionality.

Other than those corner cases, std::array should be a drop-in replacement.