[C++11][Lambda][STL][NOTE] make lambda adaptable / ptr_fun / mem_fun

ptr_fun with a lambda function
Can we get the type of a lambda argument?
Efficient Use of Lambda Expressions and std::function


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std::mem_fn
Use std::mem_fn to replace ptr_fun, mem_fun, mem_fun_ref
std::function
Use std::function to replace  std::unary_function , std::binary_function

The meaning of using this function wrapper is to make the sheer pointer to function adaptable by assigning some typedef.(Look up details of this typedef/using in ISO STD)

The unary function objects obtained from std::ref, std::cref, std::negate, std::logical_not, std::mem_fn, std::function, std::hash, or from another call to std::not1 have "argument_type" type defined, as are function objects derived from the deprecated std::unary_function.