常量提升的目的:: shared_ptr的＆LT; T＆GT;＆安培;作为函数的参数？ [英] Purpose of const boost::shared_ptr<T>& as function argument?

问题描述

我使用的是某些大型和维护良好的开源C ++库并在具有形式的构造一类定义来

I'm using a certain large and well-maintained open-source C++ library and came across a class definition having a constructor of the form

class SomeClass {
    SomeClass( const boost::shared_ptr<SomeOtherClass>& );
}

我的问题是：什么是传递一个常量的boost :: shared_ptr的＆LT点; T＆GT; 引用？是否真的有过一个的boost :: shared_ptr的与相关联的开销不可忽略的量; T＆GT; 通过值，或者是有一些其他类型的危险传递的boost :: shared_ptr的＆LT; T＆GT; 按值，我不知道的。

My question is: what's the point of passing a const boost::shared_ptr<T> by reference? Is there really a non-negligible amount of overhead associated with passing a boost::shared_ptr<T> by value, or is there some other kind of danger to passing a boost::shared_ptr<T> by value that I'm not aware of?

推荐答案

按值传递这是要复制它导致一个引用计数增加，所有线程同步。绝对不可忽略的。

Passing this by value is going to copy it which results in a reference count increment, synchronized across all threads. Definitely non-negligible.

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