Extensions

Protocol Conformance

An extension can make an existing type conform to a protocol.

Add conformance separately

passed
protocol_conformance.swift
Replay: real traced execution (multi-file project)
protocol StatusLabel {
    func statusLabel() -> String
}

struct Build {
    let passed: Bool
}

extension Build: StatusLabel {
    func statusLabel() -> String {
        return passed ? "passed" : "failed"
    }
}

let passed = true
let build = Build(passed: passed)
let label = build.statusLabel()

print(label)

protocol StatusLabel {
    func statusLabel() -> String
}

struct Build {
    let passed: Bool
}

extension Build: StatusLabel {
    func statusLabel() -> String {
        return passed ? "passed" : "failed"
    }
}

let passed = false
let build = Build(passed: passed)
let label = build.statusLabel()

print(label)

  1. passed ← true, build ← Build(passed: true)

    15let passed→ true = true  //@passed=false16let build→ Build(passed: true) = Build(passed: passedtrue)17let label = buildBuild(passed: true).statusLabel()

  2. func statusLabel() -> String

    9extension Build: StatusLabel {10    func statusLabel() -> String {11        return passedtrue ? "passed" : "failed"12    }

  3. label ← passed

    16let build = Build(passed: passed)17let label→ passed = buildBuild(passed: true).statusLabel()1819print(labelpassed)
    outputpassed

  1. passed ← false, build ← Build(passed: false)

    15let passed→ false = false16let build→ Build(passed: false) = Build(passed: passedfalse)17let label = buildBuild(passed: false).statusLabel()

  2. func statusLabel() -> String

    9extension Build: StatusLabel {10    func statusLabel() -> String {11        return passedfalse ? "passed" : "failed"12    }

  3. label ← failed

    16let build = Build(passed: passed)17let label→ failed = buildBuild(passed: false).statusLabel()1819print(labelfailed)
    outputfailed
extension conformance Protocol conformance can be declared in an extension when the required members fit better outside the original type declaration.