c++函数可以作为lvalue

An lvalue is an expression that yields an object reference, such as a variable name, an array subscript reference, a dereferenced pointer, or a function call that returns a reference.
----c++ in a nutshell
说的很清楚了，返回引用的函数可以做左值。无意中翻开这本书看到的。一直没有系统的学习C++，真的没有想到函数可以是左值.