traits: https://www.kuro5hin.org/?op=displaystory&sid=2001/3/1/72020/17594
http://www.informit.com/articles/article.aspx?p=30642&seqNum=8
https://en.wikibooks.org/wiki/More_C%2B%2B_Idioms/Non-copyable_Mixin
http://pages.cs.wisc.edu/~hasti/cs368/CppTutorial/NOTES/CLASSES-INTRO.html