cppreference.com > C/C++ Keywords > inline inline Syntax:
      inline int functionA( int i ) {
      ...
      }
The inline keyword requests that the compiler expand a given function in place, as opposed to inserting a call to that function. Functions that contain static data, loops, switch statements, or recursive calls cannot be inlined. When a function declaration is included in a class declaration, the compiler should try to automatically inline that function.