How std::initializer_list Works?

Question

I am currently studying c++11 i did not understand constructor of std::initializer_list it looks like this

constexpr initializer_list() noexcept : _First(nullptr), _Last(nullptr) {}

constexpr initializer_list(const _Elem* _First_arg, const _Elem* _Last_arg) noexcept
    : _First(_First_arg), _Last(_Last_arg) {}

But How it works with

std::initializer_list<int> v{1,2,3,4,5,6,7,8,9,0};

and i tried this

constexpr init(const _Elem* _First_arg, const _Elem* _Last_arg) noexcept
    : _First(_First_arg), _Last(_Last_arg) {}

but this shows error

init<int> ob{1,2,3,4,5,6,7,8,9,0}; //this shows error

 note: candidate: 'constexpr init<_Elem>::init(const _Elem*, const _Elem*) [with _Elem = int]'
 constexpr init(const _Elem* _First_arg, const _Elem* _Last_arg) noexcept
           ^~~~
 note:   candidate expects 2 arguments, 10 provided

and i changed {} to () like

std::initializer_list<int> v(1,2,3,4,5,6,7,8,9,0);

This shows error.

1)How std::initializer_list works?

2)What is behind {}?

Thanks.

Answer 1

std::initializer_list is special. It is impossible to write a class that could be used as a constructor argument in the same way. The language rules specify how std::initializer_list works - or rather, how constructors that accept std::initializer_list ie initializer-list constructors work. And the language implementation makes it work as specified.

PS Identifiers such as _Elem are reserved to the language implementation. Since your class init is not part of the language implementation, using reserved identifiers results in undefined behaviour. Don't use reserved identifiers.