Weird compiler error: Cannot convert parameter from 'int' to 'int &&'

Question

What on earth is going on here?
I\'m trying to create a pair of an int and a string and I can create the pair if I use \"magic values\" but can

Answer 1

make_pair does not make a pair of type pair, but rather deduces a suitable pair of reference types from its arguments to allow perfect forwarding. It's specified as

template 
pair make_pair(T1&& x, T2&& y);

for some suitable reference types V1 and V2. This only works if the argument types are deduced, so that && can decay to an lvalue reference if necessary. By specifying the template parameters explicitly, they are no longer deduced, and so the function arguments can only be rvalues.

The solution is to let the compiler deduce the types:

num_text.push_back(std::make_pair(42, std::string("Smeg")));  // Works fine
num_text.push_back(std::make_pair(42, text));                 // Works fine
num_text.push_back(std::make_pair(num, std::string("Smeg"))); // Works fine
num_text.push_back(std::make_pair(num, text));                // Works fine
num_text.push_back(std::make_pair(42, std::string("Smeg")));  // Works fine again

If you need to make a pair of a particular type, don't use make_pair, just make a pair

// Works, but perhaps with more copying than you want.
num_text.push_back(std::pair(num, text));