juxeii

auto nameByShirtNo = std::map<int, std::string>{{8, "Andres Iniesta"}};

const auto shirtNumber = 8;
const auto nameExists = nameByShirtNo.contains(shirtNumber);
if (nameExists)
{
    const auto playerName = nameByShirtNo.at(shirtNumber);
    std::cout << playerName << " wears shirt number " << shirtNumber;
} 
else

juxeii

auto foo(int n, std::string s)
{
    // ... calculate something expensive(like the answer to everything)
    return 42;
}

auto fooM(int n, std::string s)
{
    // what goes in here?
}

juxeii

template <typename T>
using AsFunction = decltype(std::function{std::declval<T>()});

#if defined(__GNUC__) || defined(__GNUG__)
// CTAD bug in gcc, see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98077
#define AS_FUNCTION(T) decltype(std::function{std::declval<T>()})
#else
#define AS_FUNCTION(T) AsFunction<T>
#endif