> On May 10, 2016, at 7:27 PM, plx via swift-evolution > <[email protected]> wrote: > > Do these return endIndex or nil on a not-found? > > Either can work with different tradeoffs; depends on what you care > about...but the choice should be justified and the alternative explained.
These return nil when no matching element is found, just like their from-the-beginning counterparts. endIndex would not be appropriate as a return value. > On May 10, 2016, at 13:54, Nate Cook via swift-evolution > <[email protected] <mailto:[email protected]>> wrote: > >> I've needed these in the past and used them in other languages—any feedback >> on this idea? >> >> Add last(where:) and lastIndex(where:) Methods to Bidirectional Collections >> The standard library should include methods for finding the last element of >> a bidirectional collection that matches a predicate, along with the index of >> that element. >> >> Motivation >> The standard library currently has (or will soon have) methods that perform >> a linear search from the beginning of a collection to find an element that >> matches a predicate: >> >> let a = [20, 30, 10, 40, 20, 30, 10, 40, 20] >> a.first(where: { $0 > 25 }) // 30 >> a.index(of: 10) // 2 >> a.index(where: { $0 > 25 }) // 1 >> Unfortunately, there is no such method that searches from the end of a >> bidirectional collection. Finding the last of particular kind of element has >> multiple applications, particularly with text, such as wrapping a long >> string into lines of a maximum length or trimming whitespace from the >> beginning and end of a string. >> >> This limitation can be worked around by using the methods above on the >> reversed collection, but the resulting code is truly dreadful. For example, >> to find the corresponding last index to a.index(where: { $0 > 25 }), this >> unholy incantation is required: >> >> (a.reversed().index(where: { $0 > 25 })?.base).flatMap({ a.index(before: $0) >> }) >> Wat. >> >> Proposed solution >> Bidirectional collections should include three new methods for symmetry with >> the existing forward-searching APIs: last(where:), lastIndex(where:), and >> lastIndex(of:), specifically for collections of Equatable elements. >> >> These additions would remove the need for searching in a reversed collection >> and allow code like the following: >> >> a.last(where: { $0 > 25 }) // 40 >> a.lastIndex(of: 10) // 6 >> a.lastIndex(where: { $0 > 25 }) // 7 >> Much better! >> >> _______________________________________________ >> swift-evolution mailing list >> [email protected] <mailto:[email protected]> >> https://lists.swift.org/mailman/listinfo/swift-evolution >> <https://lists.swift.org/mailman/listinfo/swift-evolution> > _______________________________________________ > swift-evolution mailing list > [email protected] > https://lists.swift.org/mailman/listinfo/swift-evolution
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