Abstract type: Difference between revisions

=={{header|Swift}}==

Swift uses Protocols to provide abstract type features. See [https://docs.swift.org/swift-book/documentation/the-swift-programming-language/protocols/ the docs]

A trivial example showing required properties and methods, and the means of providing a default implementation.

<syntaxhighlight lang="sml">

protocol Pet {

var name: String { get set }

var favouriteToy: String { get set }

func feed() -> Bool

func stroke() -> Void

}

extension Pet {

// Default implementation must be in an extension, not in the declaration above

func stroke() {

print("default purr")

}

}

struct Dog: Pet {

var name: String

var favouriteToy: String

// Required implementation

func feed() -> Bool {

print("more please")

return false

}

// If this were not implemented, the default from the extension above

// would be called.

func stroke() {

print("roll over")

}

}

</syntaxhighlight>