C++ Performance – Pass 64 Bit Int by Reference or Value

Prefer passing primitive types (int, char, float, ...) and POD structs that are cheap to copy (Point, complex) by value.

This will be more efficient than the indirection required when passing by reference.

See Boost's Call Traits.

The template class call_traits<T> encapsulates the "best" method to pass a parameter of some type T to or from a function, and consists of a collection of typedefs defined as in the table below. The purpose of call_traits is to ensure that problems like "references to references" never occur, and that parameters are passed in the most efficient manner possible.

There are four main cases where you should use pass-by-reference over pass-by-value:

1. If you are calling a function that needs to modify its arguments, use pass-by-reference or pass-by-pointer. Otherwise, you’ll get a copy of the argument.
2. If you're calling a function that needs to take a large object as a parameter, pass it by const reference to avoid making an unnecessary copy of that object and taking a large efficiency hit.
3. If you're writing a copy or move constructor which by definition must take a reference, use pass by reference.
4. If you're writing a function that wants to operate on a polymorphic class, use pass by reference or pass by pointer to avoid slicing.