Question

This function works fine:

std::string get_str() {
  return std::get<0>( make_tuple(std::string("hi")) );
}

But if you try to do the same thing with a trailing return type defined by decltype, the function returns a dangling rvalue reference:

auto get_str() -> decltype( std::get<0>( make_tuple(std::string("hi")) ) ) {
  return std::get<0>( make_tuple(std::string("hi")) );
}

I have a cool application of trailing return type where I’d like to use std::get. Unfortunately, the return type of std::get is an rvalue reference in this case, so decltype is just doing its job…

Do you know of a way to use the trailing return type and decltype but avoid the dangling rvalue reference?

Answer 1

You could remove the reference using the standard remove_reference type trait:

#include <string>
#include <tuple>
#include <type_traits>

auto get_str() ->
    std::remove_reference<
        decltype( std::get<0>( make_tuple( std::string("hi") ) ) )
    >::type
{
    return std::get<0>( make_tuple( std::string("hi") ) );
}