Remove duplicates determined KeyPath

Array+RemoveDuplicatesByKeyPath.swift

import UIKit
import PlaygroundSupport
import XCTest

extension Array {
  /// Remove duplicates based on `KeyPath`
  /// - Parameter keyPath: Property to determine uniqueness
  /// - Returns: `Array` of unique `Elements` based on `keyPath` argument
  /// - Complexity Time: O(n) / Space: O(n)
  func removingDuplicates<T: Hashable>(by keyPath: KeyPath<Element, T>) -> Self {
    var seen = Set<T>()
    
    return compactMap {
      guard !seen.contains($0[keyPath: keyPath]) else { return nil }
      seen.insert($0[keyPath: keyPath])
      return $0
    }
  }
  
  /// Remove duplicates based on `KeyPath`
  /// - Parameter keyPath: Property to determine uniqueness
  /// - Complexity Time: O(n) / Space: O(n)
  mutating func removeDuplicates<T: Hashable>(by keyPath: KeyPath<Element, T>) {
      self = removingDuplicates(by: keyPath)
  }
}


class RemoveDuplicatesByKeyPathTestCase: XCTestCase {
  struct Foo {
    let bar: Int
  }
  
  var array = Array(repeating: Foo(bar: 1), count: 5)
  
  override func setUp() {
    array.append(contentsOf: (2...10).map(Foo.init))
  }
  
  func testRemovingDuplicates() {
    let uniqueByKeyPathArray = array.removingDuplicates(by: \.bar)
    XCTAssertEqual(uniqueByKeyPathArray.map(\.bar), (1...10).map { $0 })
  }
    
  func testRemoveDuplicates() {
    array.removeDuplicates(by: \.bar)
    XCTAssertEqual(array.map(\.bar), (1...10).map { $0 })
  }
}

RemoveDuplicatesByKeyPathTestCase.defaultTestSuite.run()