Add `filter` and `ifSome(then:)` to Optional

palimondo · July 23, 2018, 12:41pm

What happened with this pitch?

Can we spin-off at least the non-controversial Optional.filter and drive that through SE proposal?

Erica_Sadun · July 23, 2018, 1:04pm

It may be more productive to file a bug report to request new features.

AlexanderM · July 26, 2018, 3:51am

Forgot about it, and I don't have time to cook up a proposal this week.

palimondo · August 1, 2018, 4:53pm

Let’s see if this has any legs then…

github.com/apple/swift

[SR-8437] Add filter method to Optional

opened 05:52PM - 01 Aug 18 UTC

56ed3025-6cad-4bf8-b972-9c308205a0af

feature standard library swift evolution proposal needed

| | | |------------------|-----------------|… |Previous ID | SR-8437 | |Radar | None | |Original Reporter | @palimondo | |Type | New Feature | <details> <summary>Additional Detail from JIRA</summary> | | | |------------------|-----------------| |Votes | 0 | |Component/s | Standard Library | |Labels | New Feature, LanguageFeatureRequest | |Assignee | None | |Priority | Medium | md5: 3852b2408d69c13546d326891036b911 </details> **Issue Description:** There is a [strong precedent from other programming languages](https://forums.swift.org/t/add-filter-and-ifsome-then-to-optional/8143) that have optional types to include method named `filter` that conditionally maps the optional to `nil`. The implementation is trivial: ``` java extension Optional { func filter(_ predicate: (Wrapped) throws -> Bool) rethrows -> Optional { return try flatMap { try predicate($0) ? self : nil } } } ``` Swift is currently missing this method. When pitched in Swift Evolution Forums, this method was met with no opposition. This looks like a clear omission without any downsides, that should be easy to add into Swift standard library without the need to go through lengthy Swift Evolution process.

Nope. @jrose said:

API additions always go through the Swift Evolution process.

@AlexanderM would you be fine with splitting out just the filter into its own proposal? Do you have time to do that?

BTW, this optional filter pattern is all over the SE-0222 that’s currently in review.

AlexanderM · March 30, 2019, 9:16pm

Finally made a proposal for this: API Additions to Optional (filter, ifSome, ifNone, peek)

AlexanderM · March 30, 2019, 9:17pm

Your ifSome is exactly equivalent to the existing Optional.map.