Lightweight generic cache

ThinCache.swift

//
//  ThinCache.swift
//  Planned
//
//  Created by Quinn McHenry on 4/10/16.
//  Copyright © 2016 Quinn McHenry. All rights reserved.
//


final class ThinCache<T> {
    private var cached: Optional<T>
    let generator: Void -> T
    
    init(generator: Void -> T) {
        self.generator = generator
    }
    
    func generate() -> T {
        let t = generator()
        cached = t
        return t
    }
    
    func invalidate() {
        cached = nil
    }
    
    var value: T {
        get {
            guard let cached = cached else { return generate() }
            return cached
        }
    }
    
}

// playgrounds are for playing! Paste the class above and these lines to try it out

var index = 1

func hashtagGenerator() -> String {
    index += 1
    return "#swift4eva \(index)"
}

let hashtagCache = ThinCache(generator: hashtagGenerator)

hashtagCache.value
hashtagCache.invalidate()
hashtagCache.generate()

let closureCache = ThinCache{ return "superthin \(index)" }
closureCache.value
index += 1
closureCache.value
closureCache.invalidate()
closureCache.value