Table of contents
TOC
Collapse the table of content
Expand the table of content

Lazy.CreateFromValue<'T> Extension Method (F#)

Den Delimarsky|Last Updated: 8/18/2017
|
1 Contributor

Creates a lazy computation that evaluates to the given value when forced.

Namespace/Module Path: Microsoft.FSharp.Control.LazyExtensions

Assembly: FSharp.Core (in FSharp.Core.dll)

Syntax

// Signature:
type System.Lazy with
member static CreateFromValue : Lazy<'T>

// Usage:
lazy.CreateFromValue (value)

Parameters

value Type: 'T

The input value.

Return Value

The created Lazy object.

Example

The following code example illustrates the use of the Lazy.CreateFromValue extension method. In this example, a dictionary is used to store previously computed values. When the factorial function is called, if the value is already computed, then Lazy.CreateFromValue is called with the cached result. If the value is not already computed, then Lazy.Create is used.



let cacheMap = new System.Collections.Generic.Dictionary<_, _>()
cacheMap.Add(0, 1I)
cacheMap.Add(1, 1I)

let lazyFactorial n =
    let rec factorial n =
        if cacheMap.ContainsKey(n) then cacheMap.[n] else
        let result = new System.Numerics.BigInteger(n) * factorial (n - 1)
        cacheMap.Add(n, result)
        result
    if cacheMap.ContainsKey(n) then
        printfn "Reading factorial for %d from cache." n
        Lazy.CreateFromValue(cacheMap.[n])
    else
        printfn "Creating lazy factorial for %d." n
        Lazy.Create (fun () ->
            printfn "Evaluating lazy factorial for %d." n
            let result = factorial n
            result)

printfn "%A" ((lazyFactorial 12).Force())
printfn "%A" ((lazyFactorial 10).Force())
printfn "%A" ((lazyFactorial 11).Force())
printfn "%A" ((lazyFactorial 30).Force())

Output

Creating lazy factorial for 12.
Evaluating lazy factorial for 12.
479001600
Reading factorial for 10 from cache.
3628800
Reading factorial for 11 from cache.
39916800
Creating lazy factorial for 30.
Evaluating lazy factorial for 30.
265252859812191058636308480000000

Platforms

Windows 8, Windows 7, Windows Server 2012, Windows Server 2008 R2

Version Information

F# Core Library Versions

Supported in: 2.0

See Also

Control.LazyExtensions Module (F#)

Lazy Computations (F#)

© 2019 Microsoft