constexpr

I am trying to write a constexpr find function that will return the index of a std::array containing a certain value. The function below seems to work OK except when the contained type is const char* : #include <array> constexpr auto name1() { return "name1"; } constexpr auto name2() { return "name2"; } template <class X, class V> constexpr auto find(X& x, V key) { std::size_t i = 0; while(i < x.size()) { if(x[i] == key) return i; ++i; } return i; } int main() { constexpr std::array<const char*, 2> x{{name1(), name2()}}; constexpr auto f1 = find(x, name1()); // this compiles constexpr auto f2

In C++14, since constexpr are not implicitly const anymore, can a constexpr member function modify a data member of a class: struct myclass { int member; constexpr myclass(int input): member(input) {} constexpr void f() {member = 42;} // Is it allowed? }; Yes they are, I believe this change started with proposal N3598: constexpr member functions and implicit const and eventually became part of N3652: Relaxing constraints on constexpr functions which changed section 7.1.5 paragraph 3 what is allowed in the function body from a white-list: its function-body shall be = delete, = default, or a

It is known that std::array::operator[] since C++14 is constexpr , see declaration below: constexpr const_reference operator[]( size_type pos ) const; However, it is also const qualified. This causes implications if you want to use the subscript operator of a std::array in order to assign values to your array at compile time. For example consider the following user literal: template<typename T, int N> struct FooLiteral { std::array<T, N> arr; constexpr FooLiteral() : arr {} { for(int i(0); i < N; ++i) arr[i] = T{42 + i}; } }; The above code won't compile if you try to declare a constexpr

I am trying to learn a bit more on how to use C++ constant expressions in practice and created the following Matrix class template for illustration purposes: #include <array> template <typename T, int numrows, int numcols> class Matrix{ public: using value_type = T; constexpr Matrix() : {} ~Matrix(){} constexpr Matrix(const std::array<T, numrows*numcols>& a) : values_(a){} constexpr Matrix(const Matrix& other) : values_(other.values_){ } constexpr const T& operator()(int row, int col) const { return values_[row*numcols+col]; } T& operator()(int row, int col){ return values_[row*numcols+col]; }