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fedecifedeci
authoredMay 25, 2021
Add trimmingSuffix, trimmingPrefix and mutating variants (#104)
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‎Guides/Trim.md

+20-1
Original file line numberDiff line numberDiff line change
@@ -48,6 +48,25 @@ func myAlgorithm2<Input>(input: Input) where Input: BidirectionalCollection {
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Swift provides the `BidirectionalCollection` protocol for marking types which support reverse traversal,
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and generic types and algorithms which want to make use of that should add it to their constraints.
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### >= 0.3.0
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In `v0.3.0` new methods are added to allow discarding all the elements matching the predicate at the beginning (prefix) or at the ending (suffix) of the collection.
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- `trimmingSuffix(while:)` can only be run on collections conforming to the `BidirectionalCollection` protocol.
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- `trimmingPrefix(while:)` can be run also on collections conforming to the `Collection` protocol.
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```swift
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let myString = " hello, world "
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print(myString.trimmingPrefix(while: \.isWhitespace)) // "hello, world "
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print(myString.trimmingSuffix(while: \.isWhitespace)) // " hello, world"
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```
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Also mutating variants for all the methods already existing and the new ones are added.
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```swift
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var myString = " hello, world "
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myString.trim(while: \.isWhitespace)
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print(myString) // "hello, world"
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```
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### Complexity
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Calling this method is O(_n_).
@@ -111,4 +130,4 @@ let result = input.dropFromBothEnds(while: { ... })
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// No such ambiguity here.
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let result = input.trimming(while: { ... })
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```
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```

‎Sources/Algorithms/Trim.swift

+215-3
Original file line numberDiff line numberDiff line change
@@ -7,6 +7,94 @@
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//
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// See https://swift.org/LICENSE.txt for license information
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//
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//===----------------------------------------------------------------------===//
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// trimmingPrefix(while:)
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//===----------------------------------------------------------------------===//
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extension Collection {
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/// Returns a `SubSequence` formed by discarding all elements at the start
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/// of the collection which satisfy the given predicate.
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///
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/// This example uses `trimmingPrefix(while:)` to get a substring without the white
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/// space at the beginning of the string:
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///
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/// let myString = " hello, world "
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/// print(myString.trimmingPrefix(while: \.isWhitespace)) // "hello, world "
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///
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/// - Parameters:
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/// - predicate: A closure which determines if the element should be
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/// omitted from the resulting slice.
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///
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/// - Complexity: O(*n*), where *n* is the length of this collection.
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///
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@inlinable
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public func trimmingPrefix(
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while predicate: (Element) throws -> Bool
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) rethrows -> SubSequence {
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let start = try endOfPrefix(while: predicate)
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return self[start..<endIndex]
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}
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}
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//===----------------------------------------------------------------------===//
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// trimPrefix(while:)
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//===----------------------------------------------------------------------===//
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extension Collection where Self: RangeReplaceableCollection {
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/// Mutates a `Collection` by discarding all elements at the start
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/// of it which satisfy the given predicate.
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///
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/// This example uses `trimPrefix(while:)` to remove the white
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/// space at the beginning of the string:
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///
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/// let myString = " hello, world "
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/// myString.trimPrefix(while: \.isWhitespace)
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/// print(myString) // "hello, world "
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///
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/// - Parameters:
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/// - predicate: A closure which determines if the element should be
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/// removed from the string.
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///
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/// - Complexity: O(*n*), where *n* is the length of this collection.
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///
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@inlinable
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@_disfavoredOverload
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public mutating func trimPrefix(
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while predicate: (Element) throws -> Bool
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) rethrows {
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let end = try endOfPrefix(while: predicate)
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removeSubrange(startIndex..<end)
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}
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}
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extension Collection where Self == Self.SubSequence {
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/// Mutates a `Collection` by discarding all elements at the start
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/// of it which satisfy the given predicate.
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///
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/// This example uses `trimPrefix(while:)` to remove the white
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/// space at the beginning of the string:
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///
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/// let myString = " hello, world "
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/// myString.trimPrefix(while: \.isWhitespace)
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/// print(myString) // "hello, world "
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///
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/// - Parameters:
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/// - predicate: A closure which determines if the element should be
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/// removed from the string.
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///
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/// - Complexity: O(*n*), where *n* is the length of this collection.
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///
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@inlinable
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public mutating func trimPrefix(
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while predicate: (Element) throws -> Bool
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) rethrows {
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self = try trimmingPrefix(while: predicate)
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}
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}
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//===----------------------------------------------------------------------===//
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// trimming(while:) / trimmingSuffix(while:)
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//===----------------------------------------------------------------------===//
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extension BidirectionalCollection {
@@ -29,8 +117,132 @@ extension BidirectionalCollection {
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public func trimming(
30118
while predicate: (Element) throws -> Bool
31119
) rethrows -> SubSequence {
32-
let start = try endOfPrefix(while: predicate)
33-
let end = try self[start...].startOfSuffix(while: predicate)
34-
return self[start..<end]
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return try trimmingPrefix(while: predicate).trimmingSuffix(while: predicate)
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}
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/// Returns a `SubSequence` formed by discarding all elements at the end
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/// of the collection which satisfy the given predicate.
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///
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/// This example uses `trimmingSuffix(while:)` to get a substring without the white
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/// space at the end of the string:
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///
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/// let myString = " hello, world "
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/// print(myString.trimmingSuffix(while: \.isWhitespace)) // " hello, world"
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///
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/// - Parameters:
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/// - predicate: A closure which determines if the element should be
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/// omitted from the resulting slice.
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///
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/// - Complexity: O(*n*), where *n* is the length of this collection.
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///
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@inlinable
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public func trimmingSuffix(
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while predicate: (Element) throws -> Bool
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) rethrows -> SubSequence {
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let end = try startOfSuffix(while: predicate)
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return self[startIndex..<end]
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}
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}
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//===----------------------------------------------------------------------===//
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// trim(while:) / trimSuffix(while:)
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//===----------------------------------------------------------------------===//
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extension BidirectionalCollection where Self: RangeReplaceableCollection {
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/// Mutates a `BidirectionalCollection` by discarding all elements at the start
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/// and at the end of it which satisfy the given predicate.
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///
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/// This example uses `trim(while:)` to remove the white
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/// space at the beginning of the string:
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///
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/// let myString = " hello, world "
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/// myString.trim(while: \.isWhitespace)
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/// print(myString) // "hello, world"
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///
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/// - Parameters:
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/// - predicate: A closure which determines if the element should be
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/// removed from the string.
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///
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/// - Complexity: O(*n*), where *n* is the length of this collection.
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///
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@inlinable
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@_disfavoredOverload
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public mutating func trim(
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while predicate: (Element) throws -> Bool
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) rethrows {
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replaceSubrange(startIndex..<endIndex, with: try trimming(while: predicate))
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}
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/// Mutates a `BidirectionalCollection` by discarding all elements at the end
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/// of it which satisfy the given predicate.
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///
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/// This example uses `trimSuffix(while:)` to remove the white
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/// space at the beginning of the string:
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///
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/// let myString = " hello, world "
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/// myString.trimSuffix(while: \.isWhitespace)
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/// print(myString) // " hello, world"
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///
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/// - Parameters:
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/// - predicate: A closure which determines if the element should be
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/// removed from the string.
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///
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/// - Complexity: O(*n*), where *n* is the length of this collection.
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///
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@inlinable
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@_disfavoredOverload
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public mutating func trimSuffix(
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while predicate: (Element) throws -> Bool
196+
) rethrows {
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let start = try startOfSuffix(while: predicate)
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removeSubrange(start..<endIndex)
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}
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}
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extension BidirectionalCollection where Self == Self.SubSequence {
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/// Mutates a `BidirectionalCollection` by discarding all elements at the start
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/// and at the end of it which satisfy the given predicate.
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///
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/// This example uses `trim(while:)` to remove the white
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/// space at the beginning of the string:
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///
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/// let myString = " hello, world "
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/// myString.trim(while: \.isWhitespace)
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/// print(myString) // "hello, world"
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///
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/// - Parameters:
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/// - predicate: A closure which determines if the element should be
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/// removed from the string.
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///
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/// - Complexity: O(*n*), where *n* is the length of this collection.
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///
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@inlinable
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public mutating func trim(
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while predicate: (Element) throws -> Bool
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) rethrows {
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self = try trimming(while: predicate)
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}
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/// Mutates a `BidirectionalCollection` by discarding all elements at the end
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/// of it which satisfy the given predicate.
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///
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/// This example uses `trimSuffix(while:)` to remove the white
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/// space at the beginning of the string:
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///
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/// let myString = " hello, world "
233+
/// myString.trimSuffix(while: \.isWhitespace)
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/// print(myString) // " hello, world"
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///
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/// - Parameters:
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/// - predicate: A closure which determines if the element should be
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/// removed from the string.
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///
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/// - Complexity: O(*n*), where *n* is the length of this collection.
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///
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@inlinable
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public mutating func trimSuffix(
244+
while predicate: (Element) throws -> Bool
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) rethrows {
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self = try trimmingSuffix(while: predicate)
35247
}
36248
}

‎Tests/SwiftAlgorithmsTests/TrimTests.swift

+56-7
Original file line numberDiff line numberDiff line change
@@ -13,47 +13,96 @@ import Algorithms
1313
import XCTest
1414

1515
final class TrimTests: XCTestCase {
16-
16+
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func testEmpty() {
1818
let results_empty = ([] as [Int]).trimming { $0.isMultiple(of: 2) }
1919
XCTAssertEqual(results_empty, [])
2020
}
21-
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func testNoMatch() {
2323
// No match (nothing trimmed).
2424
let results_nomatch = [1, 3, 5, 7, 9, 11, 13, 15].trimming {
2525
$0.isMultiple(of: 2)
2626
}
2727
XCTAssertEqual(results_nomatch, [1, 3, 5, 7, 9, 11, 13, 15])
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}
29-
29+
3030
func testNoTailMatch() {
3131
// No tail match (only trim head).
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let results_notailmatch = [1, 3, 5, 7, 9, 11, 13, 15].trimming { $0 < 10 }
3333
XCTAssertEqual(results_notailmatch, [11, 13, 15])
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}
35-
35+
3636
func testNoHeadMatch() {
3737
// No head match (only trim tail).
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let results_noheadmatch = [1, 3, 5, 7, 9, 11, 13, 15].trimming { $0 > 10 }
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XCTAssertEqual(results_noheadmatch, [1, 3, 5, 7, 9])
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}
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4242
func testBothEndsMatch() {
4343
// Both ends match, some string of >1 elements do not (return that string).
4444
let results = [2, 10, 11, 15, 20, 21, 100].trimming { $0.isMultiple(of: 2) }
4545
XCTAssertEqual(results, [11, 15, 20, 21])
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}
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4848
func testEverythingMatches() {
4949
// Everything matches (trim everything).
5050
let results_allmatch = [1, 3, 5, 7, 9, 11, 13, 15].trimming { _ in true }
5151
XCTAssertEqual(results_allmatch, [])
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}
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func testEverythingButOneMatches() {
5555
// Both ends match, one element does not (trim all except that element).
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let results_one = [2, 10, 12, 15, 20, 100].trimming { $0.isMultiple(of: 2) }
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XCTAssertEqual(results_one, [15])
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}
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func testTrimmingPrefix() {
61+
let results = [2, 10, 12, 15, 20, 100].trimmingPrefix { $0.isMultiple(of: 2) }
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XCTAssertEqual(results, [15, 20, 100])
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}
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func testTrimmingSuffix() {
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let results = [2, 10, 12, 15, 20, 100].trimmingSuffix { $0.isMultiple(of: 2) }
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XCTAssertEqual(results, [2, 10, 12, 15])
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}
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// Self == Self.Subsequence
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func testTrimNoAmbiguity() {
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var values = [2, 10, 12, 15, 20, 100] as ArraySlice
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values.trim { $0.isMultiple(of: 2) }
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XCTAssertEqual(values, [15])
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}
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// Self == Self.Subsequence
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func testTrimPrefixNoAmbiguity() {
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var values = [2, 10, 12, 15, 20, 100] as ArraySlice
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values.trimPrefix { $0.isMultiple(of: 2) }
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XCTAssertEqual(values, [15, 20, 100])
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}
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// Self == Self.Subsequence
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func testTrimSuffixNoAmbiguity() {
86+
var values = [2, 10, 12, 15, 20, 100] as ArraySlice
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values.trimSuffix { $0.isMultiple(of: 2) }
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XCTAssertEqual(values, [2, 10, 12, 15])
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}
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func testTrimRangeReplaceable() {
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var values = [2, 10, 12, 15, 20, 100]
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values.trim { $0.isMultiple(of: 2) }
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XCTAssertEqual(values, [15])
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}
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func testTrimPrefixRangeReplaceable() {
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var values = [2, 10, 12, 15, 20, 100]
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values.trimPrefix { $0.isMultiple(of: 2) }
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XCTAssertEqual(values, [15, 20, 100])
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}
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func testTrimSuffixRangeReplaceable() {
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var values = [2, 10, 12, 15, 20, 100]
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values.trimSuffix { $0.isMultiple(of: 2) }
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XCTAssertEqual(values, [2, 10, 12, 15])
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}
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}

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