关于本章

Function as first class citizen是一个非常有用的特性，但是C++并不直接支持这个特性，本章介绍C++中如何实现类似于function as first class citizen效果。

实现方式

在 stackoverflow What is ScopeGuard in C++? # A 中，提出了两种实现思路:

The rôle of the function here is to avoid templating so that Scope_guard instances can be declared as such, and passed around. An alternative, slightly more complex and with slightly constrained usage, but possibly marginally more efficient, is to have a class templated on a functor type, and use C++11 auto for declarations, with the scope guard instance created by a factory function.

下面是总结:

	优势	劣势
std::function	1、can be passed around	性能？
function as template parameter
function object

Function as template parameter

参见 ../Generic-programming/Function-as-template-parameter 章节。

std::function

std::function 是非常好的选择，因为它是polymorphic value type，它融合了OOP和GP的优势。

NOTE:

1、tag-std-function-polymorphic value type-融合OOP-和-GP

参见 std-function 章节。

Function object

参见 Function-objects 章节。

Application

1、AOP

一个非常重要的application就是AOP。

TO RAED

github cwrap

Auto wrap C and C++ functions with instrumentation