Swift: what's a use case for passing a primitive by reference

Question

Swift has the inout keyword to pass a primitive argument by reference. When would I use this over just passing it by value?

Edit: I realize that you can use this to change its value, but why not just pass it by value and assign it the corresponding value in the tuple returned by the function?

language allow you to do it doesn't means it is always good practice to do it — Bryan Chen, Jun 15 '14 at 21:56
It's how assignment operators are implemented: func +=(inout lhs: Int, rhs: Int) { lhs = lhs + rhs } — Jacob Lukas, Aug 31 '15 at 00:41

score 6 · Accepted Answer · answered Jun 15 '14 at 21:12

6

You would do that if you wanted to modify the original value instead of just a copy. However, I would argue that you should just return the new value since you can return multiple values in Swift.

answered Jun 15 '14 at 21:12

drewag

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I also would argue that you should just return the new value since you can return multiple values in Swift. – zaph Jun 15 '14 at 22:02

score 2 · Answer 2 · answered Jun 15 '14 at 22:38

2

This seems to be a plausible reason:

"Maybe the existing body of Objective C libraries have a lot of out parameters, and they didn't want to wrap them all for Swift."

http://blog.lexspoon.org/2014/06/my-analysis-of-swift-language.html

answered Jun 15 '14 at 22:38

tldr

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I believe that is the reason that the feature exists at all in the language. I'm not sure if that is a valid reason to create new APIs that use inout. – drewag Jun 15 '14 at 22:43

Swift: what's a use case for passing a primitive by reference

2 Answers2