Swift Resources & Notes

Swift Style Guide
Swift Cheat Sheet
"Ultimate Guide" to optionals
alternate documentation with examples
swift 5.3 language reference
an app for making swiftui apps
later…
various forms of closure syntax or what you sometimes call inline functions

2021-02-17

A little out of date but great conceptually:

Caching computed properties

Swift has computed properties; here's a pattern for caching them:

struct Cached <T, U> {
    var value : T { willSet { _calculated = nil } }
    private var _calculated : U? = nil
    private var function : (T) -> U
    
    init(_ value: T, _ f: (T) -> U) {
        self.function = f
        self.value = value
    }
    
    var calculated : U {
        mutating get {
            if _calculated == nil { _calculated = function(value) }
            return _calculated!
        }
    }
}

Example use:

var a = Cached(0) {
    (a: Int) -> Int in
    print("did calculate")
    return a + 100
}
// Prints "did calculate"

print(a.calculated)
// Prints "100"

a.value = 10

print(a.calculated)
// Prints "did calculate\n110"