If I remove elements from an array and store it in a variable like this:
let lastFive = myArray.suffix(5)
or this:
let lastFive = myArray.dropLast(5)
lastFive will be Array<SomeType>.SubSequence instead of the element type SomeType. How do I make lastFive become the [Element] rather than a SubSequence?
I like to use this extension:
extension Sequence {
func asArray() -> [Element] {
return Array(self)
}
}
That said, both the Collection and Sequence protocols define a sequence() method.
Sequence.prefix() returns [Element] while Collection.prefix() returns a SubSequence.
Given an Array defined as follows, we can do some interesting things.
let myArray = [1, 2, 3, 4, 5]
The following works because the compiler knows to use the Sequence version of suffix().
func lastFive() -> [Int] {
return myArray.suffix(5)
}
Here I'm just using the extension from above.
func lastFive2() -> [Int] {
return myArray.suffix(5).asArray()
}
The following also works because the compiler knows to use the Sequence version of suffix().
func lastFive3() -> [Int] {
let suffix: [Int] = myArray.suffix(5)
return suffix
}
This does not compile because the compiler assumes you want to use the Collection version of suffix().
func doesNotCompile() -> [Int] {
let suffix = myArray.suffix(5)
return suffix
}