4 ms·

>One of my favorite parts of Swift is the optional concept What if you need the fallback value to be an error possessing information about what went wrong?

>One of my favorite parts of Swift is the optional concept What if you need the fallback value to be an error possessing information about what went wrong? data Maybe a = Just a | Nothing data Either a b = Left a | Right b

katfang 12y ago
I agree! Eithers are cool, too. What I'm really excited about is that these sorts of concepts are starting to find their way into languages like Swift. Getting built-in support for Eithers would be super awesome. In the meantime, you can vaguely simulate it with named tuples. let response = (error: "Could not connect to server", success: false) It's not quite the same, but at least there's an easy way to bundle your data together. edit: I like Someone's suggestion to use and discussion about using enums as union types below.
- Someone 12y ago
  Other approach: use enums as union types. From https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Enumerations.html https://developer.apple.com/library/ios/documentation/Swift/...: enum Barcode { case UPCA(Int, Int, Int, Int) case QRCode(String) } This can be read as: “Define an enumeration type called Barcode, which can take either a value of UPCA with an associated value of type (Int, Int, Int, Int), or a value of QRCode with an associated value of type String.” So, you can do enum ResultOrError { case Result(ReturnValue) case Error(int,String) } Unfortunately, enums and generics do not mix, AFAIK, so it looks clumsy. I think the reason for the special syntax of '?.' is that the designers think it is a very common case, at least in Swift programs. And yes, I would like to see a better syntax for that, too. A generalization of C's short-hand 'if' flag ? trueExpression : falseExpression; For switch statements would be cool.
  - eridius 12y ago
    Enums and generics mix just fine in theory. Rust is a good example of this, with the `Result<T,E>` type. But at the moment in Swift if you try this you get "error: unimplemented IR generation feature non-fixed multi-payload enum layout". Presumably this will be supported at some point.
- bjz_ 12y ago
  > Getting built-in support for Eithers would be super awesome. Wait, what? Swift has sum types (ie. enums), so there's no need for it to be built in.
austinz 12y ago
Swift's Optional is just Maybe with some built-in sugar. Sum types are supported, with the caveat that the compiler is sort of broken when it comes to generics. Personally, I just want higher-kinded types, and for the following code snippets to work as-is: enum Either<A,B> { case Left(A) case Right(B) } enum Tree<A> { case Leaf case Node(Tree<A>, A, Tree<A>) } The first breaks because of the "Unimplemented non-fixed multi-payload enum layout" compiler error, and the second breaks because enums have value semantics. Both can be worked around in full generality by declaring a 'Box<T>' generic wrapper class, but that workaround is inelegant and cumbersome.
titaniumdecoy 12y ago
Use Swift's nil coalescing operator: a ?? b

katfang 12y ago

I agree! Eithers are cool, too. What I'm really excited about is that these sorts of concepts are starting to find their way into languages like Swift. Getting built-in support for Eithers would be super awesome. In the meantime, you can vaguely simulate it with named tuples. let response = (error: "Could not connect to server", success: false) It's not quite the same, but at least there's an easy way to bundle your data together. edit: I like Someone's suggestion to use and discussion about using enums as union types below.

Someone 12y ago
Other approach: use enums as union types. From https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Enumerations.html https://developer.apple.com/library/ios/documentation/Swift/...: enum Barcode { case UPCA(Int, Int, Int, Int) case QRCode(String) } This can be read as: “Define an enumeration type called Barcode, which can take either a value of UPCA with an associated value of type (Int, Int, Int, Int), or a value of QRCode with an associated value of type String.” So, you can do enum ResultOrError { case Result(ReturnValue) case Error(int,String) } Unfortunately, enums and generics do not mix, AFAIK, so it looks clumsy. I think the reason for the special syntax of '?.' is that the designers think it is a very common case, at least in Swift programs. And yes, I would like to see a better syntax for that, too. A generalization of C's short-hand 'if' flag ? trueExpression : falseExpression; For switch statements would be cool.
- eridius 12y ago
  Enums and generics mix just fine in theory. Rust is a good example of this, with the `Result<T,E>` type. But at the moment in Swift if you try this you get "error: unimplemented IR generation feature non-fixed multi-payload enum layout". Presumably this will be supported at some point.
bjz_ 12y ago
> Getting built-in support for Eithers would be super awesome. Wait, what? Swift has sum types (ie. enums), so there's no need for it to be built in.

austinz 12y ago

Swift's Optional is just Maybe with some built-in sugar. Sum types are supported, with the caveat that the compiler is sort of broken when it comes to generics. Personally, I just want higher-kinded types, and for the following code snippets to work as-is: enum Either<A,B> { case Left(A) case Right(B) } enum Tree<A> { case Leaf case Node(Tree<A>, A, Tree<A>) } The first breaks because of the "Unimplemented non-fixed multi-payload enum layout" compiler error, and the second breaks because enums have value semantics. Both can be worked around in full generality by declaring a 'Box<T>' generic wrapper class, but that workaround is inelegant and cumbersome.

titaniumdecoy 12y ago

Use Swift's nil coalescing operator: a ?? b