New user - accolades and questions

[benrimmington]

@adev

For instance, the documentation for Hashable doesn't really correlate to a new user experience, at least mine.

In addition to the documentation for Equatable and Hashable, there's also an article on Adopting Common Protocols and a video on What's New in Swift.

You might find the following topics useful:

Why does Hashable require Equatable?

Hashable extends Equatable because hashing is a meaningless operation without equality: the requirements on hash values are defined in terms of equal and non-equal elements. From a practical viewpoint, without Equatable, you may be able to add elements to a Dictionary or a Set, but you wouldn't be able to look them up later. This eliminates the primary purpose of these data structures. When you calculate a hash, you're distilling the original value to a fixed-width sequence of bits that can be…

Xcode 10 GM: hash(into:) issue from NSObject class

Cocoa defines its own hashing API that is independent of Swift's Hashable. To customize hashing in NSObject subclasses, the correct property to override is NSObject.hash. Trying to customize hashing by overriding hash(into:) and/or hashValue will not work correctly -- if you do that then NSDictionary, NSSet, and Foundation's other hashing collections won't work correctly with your class, often leading to severe problems. It's rather unfortunate that hash and hashValue have distinct names; the…

How is synthesized Hashable implemented?

The hash function in Swift 4.2 is SipHash-1-3; however, this is an implementation detail that is subject to change in any release. (Note that hashing changed considerably between Swift 4.1 and 4.2. I'm going to concentrate on Swift 4.2 here. Swift 4.1 uses a less robust algorithm to generate hash values, but compiler synthesis works in a roughly similar way.) The new Hasher API (introduced by SE-0206, implemented in 4.2) exposes the standard hash function as public API. It has been carefully de…

Use `Hashable.hash(into:)` or `Hasher.combine(_:)`?

Hasher's generic combine method is defined in Hasher.swift to simply call hash(into:) on its argument: @inlinable @inline(__always) public mutating func combine<H: Hashable>(_ value: H) { value.hash(into: &self) } So hasher.combine(foo) is in fact just an alternative spelling for foo.hash(into: &hasher). They are completely equivalent. Choosing one or the other is a matter of aesthetic preference. I personally prefer to use the generic combine, because it reads clearer to me. (I f…