A "fast" memoization generic in Swift

gistfile1.txt

Promised speed:

0.1s https://dl.dropboxusercontent.com/s/bpgountdjrbs17n/2014-06-09%20at%2019.00.png

Actual speed:

575s https://dl.dropboxusercontent.com/s/2kbn5p1g4t03fvl/2014-06-09%20at%2019.00%20%281%29.png

With optimizations:

$ time xcrun swift -i -Ofast memoize.swift
1.61803398874989
      608.42 real       304.25 user       144.19 sys

memoize.swift

func memoize<T: Hashable, U>( body: ( (T)->U, T )->U ) -> (T)->U {
    var memo = Dictionary<T, U>()
    var result: ((T)->U)!
    result = { x in
        if let q = memo[x] { return q }
        let r = body(result, x)
        memo[x] = r
        return r
    }
    return result
}

let fibonacci = memoize {
    fibonacci, n in
    n < 2 ? Double(n) : fibonacci(n-1) + fibonacci(n-2)
}

println(fibonacci(45)/fibonacci(44))

Hey just wrote an in depth post this, might be interested read for you random googles :) https://medium.com/@mvxlr/swift-memoize-walk-through-c5224a558194#.sl4bfon3k