AnyHashable替代AnyEquatable

Question

我需要比较符合协议P的结构数组。

[P无法符合Equatable，因为它必须没有“自我要求”。

创建AnyEquatable作为类型擦除是为此目的的常见做法。但是，AnyEquatable已经是标准库的一部分，并且符合AnyHashable。

我想知道Equatable是否不属于标准库是有充分的理由的。应该使用标准的AnyEquatable代替AnyHashable吗？

Answer 1

AnyEquatable包装了许多常用功能。那AnyHashable不是；它所做的只是一个闭包即可。

AnyEquatable

let cupcake = "🧁"
let notCake = 0xca_e

let cupcakeEquals: (Any) -> Bool = try cupcake.getEquals()
XCTAssert( cupcakeEquals(cupcake) )
XCTAssertFalse( cupcakeEquals(notCake) )

let notCakeEquals = try notCake.getEquals(Any.self)
XCTAssert( notCakeEquals(notCake) )
XCTAssertFalse( notCakeEquals(cupcake) )

XCTAssertThrowsError(
  try cupcake.getEquals() as (Int) -> Bool
)

public extension Equatable {
  /// A closure that equates another instance to this intance.
  /// - Parameters:
  ///   - _: Use the metatype for `Castable` to avoid explicit typing.
  /// - Throws: `CastError.Impossible` if a `Castable` can't be cast to `Self`.
  func getEquals<Castable>(_: Castable.Type? = nil) throws -> (Castable) -> Bool {
    if let error = CastError.Impossible(self, Castable.self)
    { throw error }

    return { self == $0 as? Self }
  }
}