I was wondering if the community would like Swift to have a switch statement with optional binding.
Take this simple dictionary as an example:
let cityIDs = ["Paris": 1, "London": 2]
Currently, this is how things are done if parisCityID is used only once within an if-let statement for only a switch statement:
if let parisCityID = cityIDs["Paris"] {
switch parisCityID {
case 0..<10:
print("Paris city ID: \(parisCityID)")
default:
break
}
}
And here is the proposed switch statement with optional binding:
switch let parisCityID = cityIDs["Paris"] {
case 0..<10:
print("Paris city ID: \(parisCityID)")
default:
break
}
With var:
switch var parisCityID = cityIDs["Paris"] {
case 0..<10:
parisCityID += 2 // just to demonstrate var
print("Paris city ID: \(parisCityID)")
default:
break
}
You can do it today (2.2 and 3.0-master) like this:
switch cityIDs["Paris"] {
case let .Some(parisCityID) where 0..<10 ~= parisCityID:
print("Paris city ID: \(parisCityID)")
default:
break
}
···
On May 27, 2016, at 1:58 AM, Natthan Leong via swift-evolution <swift-evolution@swift.org> wrote:
Hi there,
I was wondering if the community would like Swift to have a switch statement with optional binding.
Take this simple dictionary as an example:
let cityIDs = ["Paris": 1, "London": 2]
Currently, this is how things are done if parisCityID is used only once within an if-let statement for only a switch statement:
if let parisCityID = cityIDs["Paris"] {
switch parisCityID {
case 0..<10:
print("Paris city ID: \(parisCityID)")
default:
break
}
}
And here is the proposed switch statement with optional binding:
switch let parisCityID = cityIDs["Paris"] {
case 0..<10:
print("Paris city ID: \(parisCityID)")
default:
break
}
With var:
switch var parisCityID = cityIDs["Paris"] {
case 0..<10:
parisCityID += 2 // just to demonstrate var
print("Paris city ID: \(parisCityID)")
default:
break
}
However, the case statements may increase as shown below and I was wondering if it will still be worth it(Greetings core team!) in adding some syntactic sugar as aforementioned...
switch cityIDs["Paris"] {
case let .Some(parisCityID) where 0..<3 ~= parisCityID:
print("Paris city ID: \(parisCityID)")
case let .Some(parisCityID) where 3..<5 ~= parisCityID:
print("")
case let .Some(parisCityID) where 5..<10 ~= parisCityID:
fatalError()
default:
break
}
One more aspect that I have thought of is that the proposed switch statement with optional binding may only bind one value unlike if-let i.e.
if let x = foo, y = bar {
// do something with `x` and `y`
}
// but the following can't happen
switch let x = foo, y = bar {
// compile error
}
···
On May 27, 2016, at 9:25 AM, Kevin Nattinger <swift@nattinger.net> wrote:
switch cityIDs["Paris"] {
case let .Some(parisCityID) where 0..<10 ~= parisCityID:
print("Paris city ID: \(parisCityID)")
default:
break
}