Why are function templates not partial specialization?

background

C++ Classes in are not overloaded , Class templates are not overloaded , Function has overload , Function templates also have overloads , This conclusion is consistent with common sense .

// Example 1: Class vs. function template, and overloading 

// A class template
template<class T> class X {
     /*...*/ };      // (a)

// A function template with two overloads
template<class T> void f( T );              // (b)
template<class T> void f( int, T, double ); // (c)

Reference resources ：http://www.gotw.ca/publications/mill17.htm