Compacted

[Source | Tests]

A convenience method that lazily flattens the nils out of a sequence or collection.

The new method matches one of the most common uses of compactMap, which is to only remove nils without transforming the elements (e.g. collection.lazy.compactMap { $0 }).

let array: [Int?] = [10, nil, 30, nil, 2, 3, nil, 5]
let withNoNils = array.compacted()
// Array(withNoNils) == [10, 30, 2, 3, 5]

The type returned by compacted() lazily computes the non-nil elements without requiring a user to provide a closure or use the .lazy property.

Detailed Design

The compacted() methods has two overloads:

extension Sequence {
    public func compacted<Unwrapped>() -> CompactedSequence<Self, Unwrapped>
        where Element == Unwrapped? 
}

extension Collection {
    public func compacted<Unwrapped>() -> CompactedCollection<Self, Unwrapped>
        where Element == Unwrapped?
}

The Sequence version of compacted() returns a CompactedSequence type, while the Collection version returns CompactedCollection. The collection has conditional conformance to BidirectionalCollection when the base collection conforms, and both have conditional conformance to LazySequenceProtocol when the base collection conforms.

Naming

The name compacted() matches the existing method compactMap, which is commonly used to extract only the non-nil values without mapping them to a different type.