The std::apply is a compile-time helper that helps us work more agnostic about the types we handle in our code.

Imagine we have a tuple t with the values (123, "abc"s, 456.0). This tuple has the type, tuple<int, string, double>. Additionally, assume that we have a function f with the signature int f(int, string, double) (the types can also be references).

Then, we can write x = apply(f, t), which will result in a function call, x = f(123, "abc"s, 456.0). The apply method does even return to us what f returns.