std::vector<int> v;
v.emplace_back(1);
v.emplace_back({1});
v.emplace_back(int{1});

v.emplace_back({1});

#include <iostream>
#include <initializer_list>

struct A
{
    template <typename ...T>
    void f( T &&... ) const {}
};

int main()
{
    A().f( { 1 } );

    return 0;
}

prog.cpp: In function 'int main()':
prog.cpp:13:15: error: no matching function for call to 'A::f(<brace-enclosed initializer list>)'
  A().f( { 1 } );
               ^
prog.cpp:8:7: note: candidate: void A::f(T&& ...) const [with T = {}]
  void f( T &&... ) const {}
       ^
prog.cpp:8:7: note:   candidate expects 0 arguments, 1 provided

#include <iostream>
#include <initializer_list>

struct A
{
    template <typename ...T>
    void f( T &&... ) const {}
};

int main()
{
    A().f<int>( { 1 } );

    return 0;
}

#include <iostream>
#include <vector>
#include <initializer_list>

int main()
{
    std::vector<int> v;

    v.emplace_back<int>( { 1 } );

    for ( int x : v ) std::cout << x << ' ';
    std::cout << std::endl;

    return 0;
}

1

#include <iostream>
#include <vector>

struct S
{
    S(std::initializer_list<int>) {}
};

int main()
{
    std::vector<S> v;
    v.emplace_back<std::initializer_list<int>>({1});
}

v.emplace_back(int{1});