Inline Function Definitions

You can organize your inline function definitions in two ways: with definitions inline and with definitions included. Each approach has advantages and disadvantages.

Definitions Inline

You can use the definitions-inline organization only with member functions. Place the body of the function directly following the function declaration within the class definition.

class Class 
{
    int method() { return 3; }
};

This organization avoids repeating the prototype of the function, reduces the bulk of source files and the chance for inconsistencies. However, this organization can introduce implementation details into what would otherwise be read as an interface. You would have to do significant editing if the function became non-inline.

Use this organization only when the body of the function is trivial (that is, empty braces) or the function will always be inline.

Definitions Included

You can use the definitions-included organization for all inline functions. Place the body of the function together with a repeat (if necessary) of the prototype. The function definition may appear directly within the source file or be included with the source file

class Class {
    int method();
};
inline int Class::method() {
    return 3;
}

This organization separates interface and implementation. You can move definitions easily from header files to source files when the function is no longer implemented inline. The disadvantage is that this organization repeats the prototype of the class, which increases the bulk of source files and the chance for inconsistencies.