Question

#include <functional>
#include <iostream>

namespace{
//const std::function< void( const int ) > foo[] =
const auto foo[] =
{
  []( const int v ){ std::cout<<v<<std::endl; },
  []( const int v ){ std::cout<<v/2<<std::endl; },
  []( const int v ){ std::cout<<v/3<<std::endl; },
};

}

int main()
{
  foo[1](5);
}

The above example fails to compile (using g++ 4.6.1) with next error message:

error: unable to deduce 'const std::initializer_list<const auto> []' from '{{}, {}, {}}'

The commented line works fine (without specifying the function type).

Is this a quirk of g++? Or is there anything in the standard that tells the above should not compile?

Answer 1

You can’t do this. Each lambda has an unique, unrelated type. If you want a collection of lambdas, you have to erase the type with std::function:

std::function<void(int)> foo[] = {
    [](int) { ... },
    [](int) { ... },
    ...
};

Even in

auto f1 = []{};
auto f2 = []{};

the two types are different.