Default argument vs overloads in C++

Question

For example, instead of

void shared_ptr::reset() noexcept;
template 
void shared_ptr::reset(Y* ptr);

one may think of

Answer 1

There is a fundamental difference between an overload and a default pointer:

• the overload is self contained: the code in the library is completely independent of the calling context.
• the default parameter is not self contained but depend on the declaration used in the calling context. It can be redefined in a given scope with a simple declaration (e.g. a different default value, or no default value anymore.

So semantically speaking, the default value is a short-cut embeded in the calling code, whereas the overload is a meaning embedded in the called code.