Seq.readonly<'T> Function (F#)

Creates a new sequence object that delegates to the given sequence object. This ensures the original sequence cannot be rediscovered and mutated by a type cast. For example, if given an array the returned sequence will return the elements of the array, but you cannot cast the returned sequence object to an array.

Namespace/Module Path: Microsoft.FSharp.Collections.Seq

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

// Signature:
Seq.readonly : seq<'T> -> seq<'T>

// Usage:
Seq.readonly source

Parameters

• source
  Type: seq<'T>

  The input sequence.

Exceptions

Return Value

The result sequence.

Remarks

This function is named ReadOnly in compiled assemblies. If you are accessing the function from a language other than F#, or through reflection, use this name.

Example

The following code uses Seq.readonly to create an immutable view of a mutable array.

type ArrayContainer(start, finish) =
    let internalArray = [| start .. finish |]
    member this.RangeSeq = Seq.readonly internalArray
    member this.RangeArray = internalArray

let newArray = new ArrayContainer(1, 10)
let rangeSeq = newArray.RangeSeq
let rangeArray = newArray.RangeArray
// These lines produce an error:  
//let myArray = rangeSeq :> int array 
//myArray.[0] <- 0 
// The following line does not produce an error.  
// It does not preserve encapsulation.
rangeArray.[0] <- 0

Platforms

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

Version Information

F# Core Library Versions

Supported in: 2.0, 4.0, Portable

See Also

Reference

Collections.Seq Module (F#)

Microsoft.FSharp.Collections Namespace (F#)