Compile time size of data member std::array in non-class template (C++14)
The standard provides a static version of array::size
under the name tuple_size
:
#include <array>
#include <tuple> // for std::tuple_size_v
static_assert(std::tuple_size<decltype(arr_)>::value == kAnotherArraySize, "");
static_assert(std::tuple_size_v<decltype(arr_)> == kAnotherArraySize); // C++17
You can create an instance of an array with the same type of Foo::arr_
within the static assertion:
class Foo {
std::array<int, kArraySize> arr_;
static_assert(decltype(arr_){}.size() == kAnotherArraySize, "");
};
See this example.
Note: this works only if the array value type is a POD or has a default constexpr constructor.
Just to offer another option, you can do partial specialization on template variables.
#include <array>
#include <cstddef>
// Defined/provided from elsewhere.
constexpr std::size_t kArraySize = 12U;
constexpr std::size_t kAnotherArraySize = 12U;
template <typename T>
constexpr std::size_t array_size = 0;
template <typename T, std::size_t N>
constexpr std::size_t array_size<std::array<T, N>> = N;
class Foo {
std::array<int, kArraySize> arr_;
static_assert(array_size<decltype(arr_)> == kAnotherArraySize, "");
};
int main() {}