【boost】BOOST_LOCAL_FUNCTION體驗

c++11裡支持使用lambda在函數內定義本地嵌套函數，將一些算法的判斷式定義為本地函數可以使代碼更加清晰，同時聲明和調用靠近也使得更容易維護。遺憾的是公司開發平台任然停留在vs2008，使用boost庫的lambda表達式來模擬實在是有些笨拙與晦澀。

偶然在論壇上看見boost1.50版本後引入了BOOST_LOCAL_FUNCTION宏，官方簡介如下：

http://www.boost.org/doc/libs/1_54_0/libs/local_function/doc/html/boost_localfunction/tutorial.html

Local Functions

Local functions are defined using macros from the header file boost/local_function.hpp. The macros must be used from within a declarative context (this is a limitation with respect to C++11 lambda functions which can instead be declared also within expressions):

#include <boost/local_function.hpp> // This library header.

...
{ // Some declarative context.
    ...
    result-type BOOST_LOCAL_FUNCTION(parameters) {
        body-code
    } BOOST_LOCAL_FUNCTION_NAME(name)
    ...
}

使用宏的方式來定義了一個嵌套的函數（雖然只是看起來像），但是也使得我們有另一種選擇。BOOST_LOCAL_FUNCTION使用非常簡單，官方示例代碼如下：

  main() {                            
      sum = , factor = ;               
 
      BOOST_LOCAL_FUNCTION( bind factor, bind& sum,          sum += factor *  
     add();                                 
      nums[] = {,      std::for_each(nums, nums + , add);     
 
     BOOST_TEST(sum == );                  
      }