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!_______________________________________________
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