[swift-evolution] [Proposal] Use inout at function call sites

[swift at lng.la]

+1 for the same reason.

Jarod

> On Jan 29, 2016, at 14:50, Matthew Johnson via swift-evolution <swift-evolution at swift.org> wrote:
> 
> +1.  Really like the declaration and use symmetry.
> 
>> On Jan 29, 2016, at 4:48 PM, Erica Sadun via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> 
>> +1.
>> 
>> -- E
>> 
>>> On Jan 29, 2016, at 3:44 PM, Trent Nadeau via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>> 
>>> https://github.com/tanadeau/swift-evolution/blob/master/proposals/00xx-use-inout-at-func-call-site.md <https://github.com/tanadeau/swift-evolution/blob/master/proposals/00xx-use-inout-at-func-call-site.md>
>>> 
>>> # Use `inout` at Function Call Sites
>>> 
>>> * Proposal: TBD
>>> * Author(s): [Trent Nadeau](http://github.com/tanadeau <http://github.com/tanadeau>)
>>> * Status: TBD
>>> * Review manager: TBD
>>> 
>>> ## Introduction
>>> 
>>> Currently when a function has `inout` parameters, the arguments are passed with the `&` prefix operator. For example:
>>> 
>>> ```swift
>>> func add1(inout num: Int) {
>>>     num += 1
>>> }
>>> 
>>> var n = 5
>>> add1(&n) // n is now 6
>>> ```
>>> 
>>> This operator does not fit with the rest of the language nor how the parameter is written at the function declaration. It should be replaced so that `inout` is used in both locations so that the call site above would instead be written as:
>>> 
>>> ```swift
>>> add1(inout n) // symmetric and now obvious that n can change
>>> ```
>>> 
>>> *Discussion thread TBD*
>>> 
>>> ## Motivation
>>> 
>>> The `&` prefix operator is a holdover from C where it is usually read as "address of" and creates a pointer. While very useful in C due to its pervasive use of pointers, its meaning is not the same and introduces an unnecessary syntactic stumbling block from users coming from C. Removing this operator and using `inout` removes this stumbling block due to the semantic change.
>>> 
>>> This operator is also disconnected from how the function declaration is written and does not imply that the argument may (and likely will) change. Using `inout` stands out, making it clear on first read that the variable may change.
>>> 
>>> It is also possible that Swift may add Rust-like borrowing in the future. In that case, the `&` symbol would be better used for a borrowed reference. Note that Rust uses the same symbol for declaring a borrowed reference and creating one, creating a nice symmetry in that respect of the language. I think Swift would want to have such symmetry as well.
>>> 
>>> ## Detailed design
>>> 
>>> ```
>>> in-out-expression → inout identifier
>>> ```
>>> 
>>> ## Alternatives Considered
>>> 
>>> Keeping the syntax as it currently is.
>>> 
>>> -- 
>>> Trent Nadeau
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>>> swift-evolution at swift.org <mailto:swift-evolution at swift.org>
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