[swift-evolution] [swift-evolution-announce] [Review] SE-0047 Defaulting non-Void functions so they warn on unused results

Austin Zheng austinzheng at gmail.com
Thu Mar 17 03:47:25 CDT 2016

I am +1 on this proposal, which helps counter a common programmer error and encourages better-designed APIs.

Developers and users have three powerful ways to deal with this new behavior:

- Values that are meant to be optionally returned to the caller if the caller cares can be denoted by the API vendor using an inout argument of type T?.
- The API vendor can add the 'allow unused result' attribute to explicitly document that the API's semantics allow the return value to be ignored safely.
- The API consumer can use the "_ = returnsSomething()" pattern to denote that they explicitly don't care about the return value, regardless of the API vendor's intent.

Yes, it's true that any programmer can write incorrect code regardless of language features if they are sufficiently determined, but in my opinion this proposal moves the defaults towards better safety without laying a disproportionately onerous burden upon users and API vendors.


> On Mar 17, 2016, at 3:36 AM, Chris Lattner <clattner at apple.com> wrote:
> Hello Swift community,
> The review of “Defaulting non-Void functions so they warn on unused results” begins now and runs through March 21, 2016. The proposal is available here:
>    https://github.com/apple/swift-evolution/blob/master/proposals/0047-nonvoid-warn.md
> Reviews are an important part of the Swift evolution process. All reviews should be sent to the swift-evolution mailing list at:
>    https://lists.swift.org/mailman/listinfo/swift-evolution
> or, if you would like to keep your feedback private, directly to the review manager. When replying, please try to keep the proposal link at the top of the message:
> What goes into a review?
> The goal of the review process is to improve the proposal under review through constructive criticism and, eventually, determine the direction of Swift. When writing your review, here are some questions you might want to answer in your review:
>    • What is your evaluation of the proposal?
>    • Is the problem being addressed significant enough to warrant a change to Swift?
>    • Does this proposal fit well with the feel and direction of Swift?
>    • If you have used other languages or libraries with a similar feature, how do you feel that this proposal compares to those?
>    • How much effort did you put into your review? A glance, a quick reading, or an in-depth study?
> More information about the Swift evolution process is available at:
> https://github.com/apple/swift-evolution/blob/master/process.md
> Thank you,
> -Chris
> Review Manager
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