<div dir="ltr">I really think this would be a great addition to Swift. Although, I don't see the need to use a new keyword `deriving` for this feature.<div>The following would be enough:<br><div><br></div><div><div>struct Foo: Equatable, Hashable {</div><div> ...</div><div>}</div><div><br></div><div>It's explicit and it uses features already in the language. With this, the compiler would generate all the functions needed for `Foo` to conform to `Equatable` and `Hashable` and, in case the developer wants custom behavior on any of those functions, he/she could just write it from scratch and the compiler would use it over the generated one.</div></div></div><br><div class="gmail_quote"><div dir="ltr">Michael Peternell via swift-evolution <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>> escreveu no dia quinta, 26/05/2016 às 10:58:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Can we just copy&paste the solution from Haskell instead of creating our own? It's just better in every aspect. Deriving `Equatable` and `Hashable` would become<br>
<br>
struct Polygon deriving Equatable, Hashable {<br>
...<br>
}<br>
<br>
This has several advantages:<br>
- you don't have to guess wether `Equatable` or `Hashable` should be automatically derived or not.<br>
- Deriving becomes an explicit choice.<br>
- If you need a custom `Equatable` implementation (for whatever reason), you can still do it.<br>
- It doesn't break any code that is unaware of the change<br>
- It can be extended in future versions of Swift, without introducing any new incompatibilities. For example, `CustomStringConvertible` could be derived just as easily.<br>
- It is compatible with generics. E.g. `struct Shape<T> deriving Equatable` will make every `Shape<X>` equatable if `X` is equatable. But if `X` is not equatable, `Shape<X>` can be used as well. (Unless `X` is not used, in which case every `Shape<T>` would be equatable. Unless something in the definition of `Shape` makes deriving `Equatable` impossible => this produces an error.)<br>
- It is proven to work in production.<br>
<br>
-Michael<br></blockquote><div><span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13px"><br></span></div><div><span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13px">Pedro Vieira</span><br></div><div style="font-size:13px;color:rgb(34,34,34);font-family:arial,sans-serif"><a href="http://pedrovieira.me/">http://pedrovieira.me</a></div></div></div><div dir="ltr">-- <br></div><div data-smartmail="gmail_signature"><div dir="ltr"><span style="color:rgb(34,34,34);font-family:arial,sans-serif">Pedro Vieira</span><div style="color:rgb(34,34,34);font-family:arial,sans-serif"><a href="http://pedrovieira.me/">http://pedrovieira.me</a></div></div></div>