jeudi 20 octobre 2016

Forcing std::vector overload instead of int overload on list with one element

Consider the code below:

#include <iostream>
#include <vector>

void f(std::vector<int> v) {std::cout << __PRETTY_FUNCTION__ << std::endl;}
void f(int n) {std::cout << __PRETTY_FUNCTION__ << std::endl;}

int main()
{
    f({42}); // the int overload is being picked up
}

Live on Coliru

I was a bit surprised to realize that in this case the int overload is being picked up, i.e. the output of the program is:

void f(int)

with the warning

warning: braces around scalar initializer [-Wbraced-scalar-init] f({42});

Of course this happens only when I pass a 1-element list as an argument, otherwise the std::vector overload is being picked up.

Why is {42} treated like a scalar and not like a init-list? Is there any way of forcing the compiler to pick the std::vector overload even on 1-element lists?

PS: The std::vector has an init-list constructor

vector(std::initializer_list<T> init, const Allocator& alloc = Allocator());

see (7) from cppreference.

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