add self-througt information about making interfaces easy to use
correctly and hard to use incorrectly.
add self-througt information about treating class design as type design
Merge branch 'master' of https://github.com/ASMlover/study
add self-througt information perfering pass by reference to const to
pass by value
add self-througt information about do not try to return a reference when
you must an object