Trailing return type in C++14

Question

With the introduction of auto return type in C++14, is there any real situation that trailing return type is required or it's completely obsolete in C++14 and 17?

Answer 1

Consider...

auto f(int x)
{
    if (x == 2)
        return 3;
    return 2.1;
}

...this has an ambiguous return type - int or double. An explicit return type - whether prefixed or trailing - can disambiguate it and casts the return argument to the return type.

Trailing return types specifically are also useful if you want to use decltype, sizeof etc on some arguments:

auto f(int x) -> decltype(g(x))
{
    if (x == 2)
        return g(x);
    return 2;
}