Implement "If", "Else", and "ElseIf" in Swift

IfElse.swift

// Implementation of If, ElseIf, and Else in Swift.
//
// Supports uses such as these:
//
// If (condition) { doAction() }
//
// If (condition) { doAction() }
// .Else { doOtherAction() }
//
// If (condition) { doAction() }
// .ElseIf (condition1) { doAction2() }
// .ElseIf (conditionN) { doActionN() }
// .Else { doOtherAction() }

import Foundation

/// Object that processes whatever comes after an If() or ElseIf()
protocol ElseContext {
    func Else(_ action: () -> ())

    @discardableResult
    func ElseIf(_ condition: @autoclosure () -> Bool, _ action: () -> ()) -> ElseContext
}

struct If {
    /// If the If condition is false, then ContinueElse will execute
    /// the Else part or go on to the next ElseIf.
    struct ContinueElses: ElseContext {
        func Else(_ action: () -> ()) {
            action()
        }

        @discardableResult
        func ElseIf(_ condition: @autoclosure () -> Bool, _ action: () -> ()) -> ElseContext {
            if condition() {
                action()
                return SkipElses()
            }
            else {
                return ContinueElses()
            }
        }
    }

    /// If the If condition is true, then remaining ElseIf/Else items
    /// will do nothing.
    struct SkipElses: ElseContext {
        func Else(_ action: () -> ()) {}

        @discardableResult
        func ElseIf(_ condition: @autoclosure () -> Bool, _ action: () -> ()) -> ElseContext {
            return self
        }
    }

    let elseContext: ElseContext

    init(_ condition: Bool, _ action: () -> ()) {
        if condition {
            elseContext = SkipElses()
            action()
        }
        else {
            elseContext = ContinueElses()
        }
    }

    func Else(_ action: () -> ()) {
        elseContext.Else(action)
    }

    @discardableResult
    func ElseIf(_ condition: @autoclosure () -> Bool, _ action: () -> ()) -> ElseContext {
        return elseContext.ElseIf(condition, action)
    }
}

// Example

func testValue(_ value: Int) {
    If (value % 2 == 0) {
        print("\(value) is even")
    }
    .Else {
        print("\(value) is odd")
    }

    If (value > 0) {
        print("\(value) is positive")
    }
    .ElseIf (value < 0) {
        print("\(value) is negative")
    }
    .Else {
        print("\(value) is zero")
    }
}

testValue(-10)
testValue(-3)
testValue(0)
testValue(5)
testValue(12)

// Output:
// -10 is even
// -10 is negative
// -3 is odd
// -3 is negative
// 0 is even
// 0 is zero
// 5 is odd
// 5 is positive
// 12 is even
// 12 is positive