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While I think it's good to loose `var` for parameters, the different semantics for Structs and Classes can be confusing sometimes. It is not always obvious at caller site, whether you are passing a Struct or a Class instance, and therefore whether the call
will alter the instance at caller site.
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<div class="">On 16.12.2015, at 03:33, Dennis Lysenko via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:</div>
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Can you run the same survey with an example that uses a struct called "Song" instead? I think the confusion would lie in complex value types. Int may be an unideal example. <br class="">
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<div dir="ltr" class="">On Tue, Dec 15, 2015, 5:27 PM Francisco Costa via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:<br class="">
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<div class="">Hello all,<br class="">
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There is currently a proposal to remove `var` from Function Parameters and Pattern Matching which seems to have been already accepted<br class="">
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<a href="https://github.com/apple/swift-evolution/blob/master/proposals/0003-remove-var-parameters-patterns.md" target="_blank" class="">https://github.com/apple/swift-evolution/blob/master/proposals/0003-remove-var-parameters-patterns.md</a><br class="">
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I cannot find the discussion on it, probably because it predates the open sourcing of Swift. While some of its arguments may sound reasonable, I think they have been greatly exaggerated.<br class="">
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The main point of the proposal seems to be that the `var` attribute can be easily confused with `inout`. It then provides examples where `var` would be completely useless:<br class="">
<br class="">
```<br class="">
<span style="font-family: monospace, monospace;" class="">func foo(i: Int) {<br class="">
i += 1 // Illegal<br class="">
}<br class="">
<br class="">
func foo(var i: Int) {<br class="">
i += 1 // Legal but useless since we are not using this local value anywhere<br class="">
}<br class="">
</span></div>
<div class="">```<br class="">
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<div class="">We today made a quick survey around the backend developers on the office (not familiar with Swift) and not a single one suggested that the second method would mutate the original parameter value. In fact, to all of them it was clear that `var`
creates a local copy of the value and that the method is also missing a `return` if we want to use the incremented value.<br class="">
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<div class="">The Swift Language Guide gives a good explanation on this as well:<br class="">
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"Variable parameters ... give a new modifiable copy of the parameter’s value for your function to work with."<br class="">
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<div class="">This is probably a concept most beginners to the language can either guess intuitively or learn in a couple of seconds.<br class="">
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<div class="">Especially taking into account that the way we use `inout` parameters is so much advertised in Swift, to the point where calling a method with them requires to explicitly identify them with `&`, it seems that by giving up the `var` attribute we
would lose a convenient elegance in exchange for no real benefit to beginners.<br class="">
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<div class="">In fact, in my experience the `var` attribute is most often used in scenarios where immutability is intentionally preserved, we pass a immutable value to a method and it returns another immutable (modified) version of that value.<br class="">
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<div class="">Another common scenario is when you need to further modify a value that was unwrapped from an Optional. I would argue that this seems elegant and easy to read:<br class="">
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```<br class="">
<span style="font-family: monospace, monospace;" class="">if var x = getOptionalInt() {<br class="">
x += 1<br class="">
return x<br class="">
}</span><br class="">
```<br class="">
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While this (as has been proposed) seems like we are fighting a language limitation:<br class="">
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```<br class="">
<span style="font-family: monospace, monospace;" class="">if let x = getOptionalInt() {<br class="">
var x = x<br class="">
x += 1<br class="">
return x<br class="">
}</span><br class="">
```<br class="">
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<div class="">I understand that discussing back and forth proposals that have been already accepted is counter-productive, but since this discussion doesn't seem to have been published, I would kindly ask if we can give it a second thought :)<br class="">
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<div class="">Thanks,<br class="">
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<div class="">Francisco<br class="">
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