C++的RAII在WebKit中的应用

先看下面这段WebKit中的代码:

{
    NestingLevelIncrementer nestingLevelIncrementer(m_scriptNestingLevel);
    //Do something else...
}

看看NestingLevelIncrementer的实现，就知道与另一种写法看似是等价的:

{
    ++m_scriptNestingLevel;
    //Do something else...
    --m_scriptNestingLevel;   }

上面的实现是不是用加一个类的代价解决了一个简单的问题？其实是应用了C++里一个重要的概念RAII (*关键是后续执行有没有可能抛出exception)，更为典型的是WebKit中大量MutexLocker的使用。

什么是RAII (来自Stackoverflow的回复):

C++ does not support 'finally' blocks. The reason is that C++ instead supports RAII: "Resource Acquisition Is Initialization". The idea is that an object's destructor is responsible for freeing resources. When the object has automatic
storage duration, the object's destructor will be called when the block in which it was created exits -- even when that block is exited in the presence of an exception.

(原文地址)

附篇资料可以快速了解:

  RAII惯用法：C++资源管理的利器

附个PPT资料: WebKit中的两个小设计

更多的C++ idioms: More C++ idioms