[swift-users] if-case syntax ambiguity

[Zhao Xin]

The `if case` is the same meaning as `switch-case`, so I don't think there
is anything ambitious. For `switch-case`, it is not equal, it is matching.

Zhaoxin

On Wed, Nov 9, 2016 at 7:17 PM, Nicholas Outram via swift-users <
swift-users at swift.org> wrote:

> Hi
>
> I’ve been drilling down on the syntax of enumerated types with associated
> data in the current release version of Swift 3.
> I’ve pasted below a section of a Playground that captures an issue I’d
> like to raise.
>
> In summary:
>
> Consider the following
> enum Vehicle {
>    case car(petrol: Bool, sizeCC: Int)
>    case plane(engines : Int)
>    case other(String)
>    case none
> }
> let myJourney : Vehicle = .other("pogo stick")
>
> *Whereas the following is clear*
> if case .other(_) = myJourney
>
> *the following shorthand equivalent is potentially confusing for the sake
> of 3 characters*
> if case .other = myJourney
>
> - In the first case, the presence of the underscore does communicate that
> something is being assigned, but dropped.
> - In the second case, the reader could easily be mislead into thinking
> that = was supposed to be == as there no apparent place to assign anything.
>
> My suggestion would simply be to drop the shorthand as it’s ambiguous?
>
>
> Nick Outram
>
>
>
>
> import Foundation
>
> //: Consider the following enumerated type with associated data
> enum Vehicle {
>    case car(petrol: Bool, sizeCC: Int)
>    case plane(engines : Int)
>    case other(String)
>    case none
> }
>
> //: Let's pick an example
> let myJourney : Vehicle = .other("pogo stick")
>
> //: I now want to test what case `myJourney` is.
> //:
> //: We cannot use the `==` operator because `Vehicle` has associated data.
> Instead we use `if case` and *simply drop the associated value* with `_` as
> shown above
> if case .other(_) = myJourney {
>    print("Somewhere nice?")
> } else {
>    print("Ok, it's a secret?")
> }
> //:The above is clear enough once you get used to the syntax. The `_`
> communicates that a value has been dropped.
> //:
> //: **However**, Swift 3 allows us to drop the parenthesis altogether and
> use the following shorthand:
> if case .other = myJourney {
>    print("Somewhere nice?")
> } else {
>    print("Ok, it's a secret?")
> }
> //: *Unlike the previous example, I do wonder if this is a language
> feature that needs review?*
> //:
> //: - On face value, reading this code as is there is an assignment
> operator `=` with nothing apparently being assigned.
> //: - It also reads as if `=` should be `==`
>
>
>
>
>
>
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>
>
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