原文链接 https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#es56-write-stdmove-only-when-you-need-to-explicitly-move-an-object-to-another-scope
std::move and std::forward (https://stackoverflow.com/questions/9671749/whats-the-difference-between-stdmove-and-stdforward
what-are-rvalues-lvalues-xvalues-glvalues-and-prvalues [5] https://stackoverflow.com/questions/9671749/whats-the-difference-between-stdmove-and-stdforward