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

palimondo · August 1, 2018, 4:53pm

Let’s see if this has any legs then…

[SR-8437] Add filter method to Optional

opened 05:52PM - 01 Aug 18 UTC

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.