HashableBox

HashableBox.swift

/// Box for exposing an item as a hashable.
public struct HashableBox<T, H: Hashable>: Hashable {
    /// The wrapped item.
    public let item: T

    private let accessor: (T) -> H

    /// Create a new hashable box for `item` where `accessor` defines the hashable content.
    public init(_ item: T, accessor: @escaping (T) -> H) {
        self.item = item
        self.accessor = accessor
    }

    fileprivate var hashableItem: H {
        return accessor(item)
    }
    
    public var hashValue: Int {
        return hashableItem.hashValue
    }
}    
public func ==<T, H: Hashable>(lhs: HashableBox<T, H>, rhs: HashableBox<T, H>) -> Bool {
    return lhs.hashableItem == rhs.hashableItem
}