Any way to stop a block literal in swift
Since you want to stop on the first match, you should use first
and not forEach
:
numbers.first { (number) -> Bool in
return number % 2 == 0
}
Do something with the result (the first even number on the list):
if let firstEvenNumber = numbers.first(where: { $0 % 2 == 0 }) {
print("The first even number on the list is \(firstEvenNumber)")
}
Bonus: create a list of all the even numbers using filter
:
let allEvenNumbers = numbers.filter { $0 % 2 == 0 }
The document has explained。
/// - Note: You cannot use the `break` or `continue` statement to exit the
/// current call of the `body` closure or skip subsequent calls.
/// - Note: Using the `return` statement in the `body` closure will only
/// exit from the current call to `body`, not any outer scope, and won't
/// skip subsequent calls.
But you would like to try this.
extension CollectionType {
/// Use as
///
/// let num = [1,2,3,4,5]
/// num.forEach{
/// if $1 > 3 { $2 = true }
/// print($0,$1)
/// }
func forEach(body: ((Self.Generator.Element, Int, inout Bool) -> Void)) {
var stop = false
let enumerate = self.enumerate()
for (index,value) in enumerate {
if stop { break }
body(value,index,&stop)
}
}
/// Use as
///
/// let num = [1,2,3,4,5]
/// num.forEach{
/// if $0 > 3 { $1 = true }
/// print($0)
/// }
func forEach(body: ((Self.Generator.Element, inout Bool) -> Void)) {
var stop = false
for value in self {
if stop { break }
body(value,&stop)
}
}
}
forEach
is not a loop (it is a block passed to a loop, but not a loop itself), or more accurately, forEach
is not part of Swift's Control Flow. Which is why you can't use break
or continue
.
Just use a for-in loop.
Example :
var numbers = [ 1,2,3,4]
func firstEvenNumber(inArray array: [Int]) -> Int? {
var firstMatch : Int?
for number in numbers {
if (number % 2) == 0 {
firstMatch = number
break
}
}
return firstMatch
}
firstEvenNumber(inArray: numbers) // 2
You can use return
inside the forEach
closure, but it does not break the loop, it only returns the block in the current pass.
var numbers = [ 1,2,3,4]
func evenNumbers(inArray: [Int]) -> [Int] {
var matches : [Int] = []
numbers.forEach{
if $0 % 2 == 0 {
matches.append($0)
// early return on even numbers
// does not stop forEach
// comparable to a continue in a for in loop
return
}
// only reached on uneven numbers
}
return matches
}
evenNumbers(numbers) // [2,4]