c++ - What's the correct way to initialize a member array with an initializer list? -

i have struct holds array, , i'd pass initializer list struct's constructor forwarded on array. illustrate, tried:

#include <initializer_list>  struct vector {     float v[3];      vector(std::initializer_list<float> values) : v{values} {} };  int main() {     vector v = {1, 2, 3}; } 

which resulted in error:

error: cannot convert ‘std::initializer_list<float>’ ‘float’ in initialization

i tried using parentheses instead of braces v gave error:

error: incompatible types in assignment of ‘std::initializer_list<float>’ ‘float [3]’

my main motivation trying avoid following warning clang generates:

template <int n> struct vector {     float v[n]; };  template <> struct vector<2> {     float x, y; };  int main() {     vector<2> v2 = {1.0f, 2.0f};         // yay, works     vector<3> v3 = {1.0f, 2.0f, 3.0f};   // results in warning in clang++     vector<3> u3 = {{1.0f, 2.0f, 3.0f}}; // must use 2 braces avoid warning     // if make vector<n> take initializer list in constructor,     // forward on member array , avoid using double braces } 

warning: suggest braces around initialization of subobject

so question is: how can initialize member array initializer list? (i.e. how can make first code work? or not possible?

if class aggregate, can use syntax

template < std::size_t len > struct vector {     float elems[len]; };  vector<3> v = {1.0f, 2.0f, 3.0f}; 

note: possible due brace-elision. no need v = {{1,2,3}}; though possible. clang issues warning because clearer , less error-prone syntax double braces (one initializing v , 1 initializing sub-aggregate elems).

if class not aggregate, can use variadic templates:

#include <array> #include <cstddef>  template < std::size_t len > struct vector {     std::array < float, len > m;  // works raw array `float m[len];`      template < typename... tt >     vector(tt... pp) : m{{pp...}}     {}      // better, using perfect forwarding:     // template < typename... tt >     // vector(tt&&... pp) : m{{std::forward<tt>(pp)...}}     // {} };  vector<3> = {1.0f, 2.0f, 3.0f};