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在C ++中澄清[[pure]]

[英]Clarification of [[pure]] in C++

原文 2013-10-09 20:57:51 8 1 c++/ c++14

Reading the most recent proposal for a standard C++ attribute [[pure]] I was left with a number of questions: 阅读标准C ++属性[[pure]]的最新提议，我留下了许多问题：

Could a [[pure]] function read const globals? 一个[[pure]]函数可以读取const全局吗？
Could a [[pure]] function read static const variables? 一个[[pure]]函数可以读取静态const变量吗？
Could a [[pure]] function write but not read pointer or reference variables (and still return void possibly)? 一个[[pure]]函数可以写但不能读取指针或引用变量（并且仍然可能返回void）？

1 个解决方案

[[pure]], If I recall right, needs to be 100% certain that a particular input should always return a specific output. [[pure]]，如果我没记错，需要100％确定特定输入应该始终返回特定输出。 Considering a const globals and static const globals should never change states, it should be ok. 考虑一个const全局变量和静态const全局变量应该永远不会改变状态，它应该没问题。 Finally, reading a pointer that could change states would not be a pure function. 最后，读取可能改变状态的指针不是一个纯函数。 If you write to pointers accessed elsewhere, then it has a side effect and is not [[pure]]. 如果你写入其他地方访问的指针，那么它有副作用，而不是[[纯]]。

You have to ask yourself if the function result is dependent on an extraneous variables' state, and if you answer yes, it is not [[pure]]. 你必须问自己函数结果是否依赖于一个无关变量的状态，如果你回答是，那就不是[[pure]]。 You also have to ask yourself if an input can have an effect on anything other than it's return value. 您还必须问自己输入是否会对除返回值以外的任何内容产生影响。 If that is true, then it is not [[pure]] 如果这是真的，那就不是[[纯]]