47 lines
1.2 KiB
Markdown
47 lines
1.2 KiB
Markdown
---
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title: Generics
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---
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# Generics
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Write a name inside angle brackets to make a generic function or type.
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```Swift
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func makeArray<Item>(repeating item: Item, numberOfTimes: Int) -> [Item] {
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var result = [Item]()
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for _ in 0..<numberOfTimes {
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result.append(item)
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}
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return result
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}
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makeArray(repeating: "knock", numberOfTimes: 4)
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```
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***You can make generic forms of functions and methods, as well as classes, enumerations, and structures.***
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```Swift
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// Reimplement the Swift standard library's optional type
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enum OptionalValue<Wrapped> {
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case none
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case some(Wrapped)
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}
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var possibleInteger: OptionalValue<Int> = .none
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possibleInteger = .some(100)
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```
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Use `where` right before the body to specify a list of requirements—for example, to require the type to implement a protocol, to require two types to be the same, or to require a class to have a particular superclass.
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```swift
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func anyCommonElements<T: Sequence, U: Sequence>(_ lhs: T, _ rhs: U) -> Bool
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where T.Element: Equatable, T.Element == U.Element
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{
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for lhsItem in lhs {
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for rhsItem in rhs {
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if lhsItem == rhsItem {
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return true
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}
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}
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}
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return false
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}
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anyCommonElements([1, 2, 3], [3])
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