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memoizeBy

Sometimes you might wish to memoize a function whose input doesn't have the equality and comparison constraints, or maybe the comparison of your given type is just too slow for what you need. To fix this, you simply provide a function which converts the input into something more fitting as an extra parameter.

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// Note that Dictionary lookups are to be much faster than F#'s map and so should
// be used when writing library code.

let memoizeBy inputToKey f =
    let cache = Dictionary<_, _>()
    fun x ->
        let k = inputToKey x
        if cache.ContainsKey(k) then cache.[k]
        else let res = f x
             cache.[k] <- res
             res

// Example: 

open System

/// a cached version of Type.GetGenericArguments()
let cachedGetGenericArguments : Type -> Type[] =
    memoizeBy (fun t -> t.FullName) (fun t -> t.GetGenericArguments())

val memoizeBy : inputToKey:('a -> 'b) -> f:('a -> 'c) -> ('a -> 'c)

Full name: Script.memoizeBy

val inputToKey : ('a -> 'b)

val f : ('a -> 'c)

val cache : obj

val x : 'a

val k : 'b

val res : 'c

namespace System

val cachedGetGenericArguments : (Type -> Type [])

Full name: Script.cachedGetGenericArguments

a cached version of Type.GetGenericArguments()

type Type =
  inherit MemberInfo
  member Assembly : Assembly
  member AssemblyQualifiedName : string
  member Attributes : TypeAttributes
  member BaseType : Type
  member ContainsGenericParameters : bool
  member DeclaringMethod : MethodBase
  member DeclaringType : Type
  member Equals : o:obj -> bool + 1 overload
  member FindInterfaces : filter:TypeFilter * filterCriteria:obj -> Type[]
  member FindMembers : memberType:MemberTypes * bindingAttr:BindingFlags * filter:MemberFilter * filterCriteria:obj -> MemberInfo[]
  ...

Full name: System.Type

val t : Type

property Type.FullName: string

Type.GetGenericArguments() : Type []

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More information

Link:	http://fssnip.net/63
Posted:	13 years ago
Author:	Rick Minerich
Tags:	memoize , memoization , functions , utility