Question about Time.hpp

[GWD]

I am currently learning C++ and SFML 2.0.  And I think I must lack some C++ knowledge because in the file Time.hpp ( http://www.sfml-dev.org/documentation/2.0/Time_8hpp_source.php )  I cannot understand why the following non-member operator functions are not declared as friend functions....

SFML_SYSTEM_API Time& operator +=(Time& left, Time right);

SFML_SYSTEM_API Time& operator -=(Time& left, Time right);

SFML_SYSTEM_API Time& operator *=(Time& left, float right);

SFML_SYSTEM_API Time& operator *=(Time& left, Int64 right);

SFML_SYSTEM_API Time& operator /=(Time& left, float right);

SFML_SYSTEM_API Time& operator /=(Time& left, Int64 right);

Since they are not friend functions, how can they mutate a Time object, when the Time class does not feature any public mutator functions, and the m_microseconds data member is private?

[Nexus]

Please post in Help/System (for time), and use C++ code tags.

There is no point to declare the operators as friends of sf::Time, since they can be implemented using the public API. Why didn't you have a look at Time.cpp?

[eXpl0it3r]

As Nexus said the implementation is in the Time.cpp file, e.g. see on GitHub.