返回两个值，元组与“输出"与“结构" [英] Returning two values, Tuple vs 'out' vs 'struct'

问题描述

考虑一个返回两个值的函数.我们可以这样写:

Consider a function which returns two values. We can write:

// Using out:
string MyFunction(string input, out int count)

// Using Tuple class:
Tuple<string, int> MyFunction(string input)

// Using struct:
MyStruct MyFunction(string input)

哪种是最佳实践，为什么?

Which one is best practice and why?

推荐答案

它们每个都有各自的优缺点.

They each have their pros and cons.

Out参数既快速又便宜，但是需要您传入一个变量，并且要依赖突变.在LINQ上正确使用out参数几乎是不可能的.

Out parameters are fast and cheap but require that you pass in a variable, and rely upon mutation. It is almost impossible to correctly use an out parameter with LINQ.

故障堆会增加垃圾收集压力，并且无法自我记录."Item1"不是很具描述性.

Tuples make garbage collection pressure and are un-self-documenting. "Item1" is not very descriptive.

如果自定义结构很大，则复制起来可能会很慢，但如果它们很小，则可以自我记录，并且效率很高.但是，定义一堆用于琐碎用途的自定义结构也很麻烦.

Custom structs can be slow to copy if they are large, but are self-documenting and are efficient if they are small. However it is also a pain to define a whole bunch of custom structs for trivial uses.

在其他所有条件相同的情况下，我倾向于定制结构解决方案.更好的方法是制作一个仅返回一个值的函数.为什么首先要返回两个值?

I would be inclined to the custom struct solution all other things being equal. Even better though is to make a function that only returns one value. Why are you returning two values in the first place?

更新:请注意，在撰写本文后六年，C#7中的元组是值类型，因此不太可能产生收集压力.

UPDATE: Note that tuples in C# 7, which shipped six years after this article was written, are value types and hence less likely to create collection pressure.

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