[swift-evolution] ternary operator ?: suggestion

[Alex Lew]

What if we left the if { ...} else { ... } syntax alone (as a statement),
and updated the ternary expression to be a more general pattern matching
expression (closer to "switch")? Something like

let x = condition ?
   true: "Hello"
   false: "Goodbye"

let x = optionalValue ?
   .Some(let unwrapped): "Hello, \(unwrapped)"
   .None: "To Whom It May Concern"

let myFavoriteColor = yourFavoriteColor ?
    .Blue: .Red
    .Green: .Blue
    .Red: .Green

let quadrant = (x, y) ?
    let (x, y) where x < 50 && y < 50: "top left"
    let (x, y) where x < 50 && y > 50: "bottom left"
    let (x, y) where x > 50 && y < 50: "top right"
    default: "bottom right"

The colon comes from the fact that this is sort of a light-weight
expression-based "switch" statement, where each branch can only contain an
expression, not a series of statements.

This is very similar to pattern matching expressions in languages like
Haskell, ML, and Coq.

On Sun, Dec 6, 2015 at 11:25 AM, Thorsten Seitz <thorsten.seitz at web.de>
wrote:

> Am 06.12.2015 um 01:28 schrieb Alex Lew via swift-evolution <
> swift-evolution at swift.org>:
>
> I don't think you can just get rid of the if statement in favor of an
> expression. You still want to be able to do this:
>
> if (condition) {
>     funcWithSideEffectsThatReturnsInt()
> } else {
>     funcWithSideEffectsThatReturnsString()
> }
>
> but that's not a valid expression (what is its type?).
>
>
> That would actually be no problem if Swift’s type system would have union
> types (Ceylon has union and intersection types which are quite awesome and
> enable lots of nice things quite naturally, see
> http://ceylon-lang.org/documentation/1.2/tour/types/).
>
> In that case the type of such an expression would just be the union of
> both types, which is written Int | String in Ceylon.
>
> -Thorsten
>
>
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