Alexander Momchliov Alexander Momchliov - 3 months ago 7
Swift Question

Pattern match and conditionally bind in a single Switch statement

Is there a way to write this

if
/
else if
/
else
ladder as a switch statement?

let x: Any = "123"

if let s = x as? String {
useString(s)
}
else if let i = x as? Int {
useInt(i)
}
else if let b = x as? Bool {
useBool(b)
}
else {
fatalError()
}


Here's my attempt:

switch x {
case let s where s is String: useString(s)
case let i where i is Int: useInt(i)
case let b where b is Bool: useBool(b)
default: fatalError()
}


It successfully chooses the right path, but
s
/
i
/
b
are still of type
Any
. The
is
check doesn't have any effect in casting them. This forces me to force cast with
as!
before usage.

Is there a way to switch on the type, and bind it to a name, all in one
switch
statement?

Answer

Sure, you can use the conditional casting pattern case let x as Type:

let x: Any = "123"

switch x {
case let s as String:
    print(s)   //use s
case let i as Int:
    print(i)   //use i
case let b as Bool:
    print(b)   //use b
default:
    fatalError()
}
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