To be used for transduction from sequences of arbitrary objects to byte streams.

SeqStream.fs

module SeqStream

/// Reads a specified number of values from an enumeration into a buffer array.
let fillBuffer (enum:System.Collections.Generic.IEnumerator<_>) (buffer:_ array) offset count =
    let mutable read = 0
    while enum.MoveNext() && read < count do
        buffer.[read + offset] <- enum.Current
        read <- read + 1
    read

/// A read-only stream which wraps an enumerator of a byte sequence.
type ByteEnumeratorStream (enumerator:System.Collections.Generic.IEnumerator<byte>) =
    inherit System.IO.Stream()
       
    let mutable position = 0L

    override __.Read(buffer,offset,count) = 
        let read = fillBuffer enumerator buffer offset count
        position <- position + (read |> int64)
        read

    override __.CanRead = true        
    override __.CanSeek = false        
    override __.CanWrite = false        
    override __.Flush() = ()
    override __.Dispose(disposing) = enumerator.Dispose()        
    override __.Length = 0L        
    override __.Position with get () = position and set value = failwith "Can't set position!"
    override __.Seek(offset, origin) = failwith "Can't seek!"
    override __.Write(bugger,offset,count) = failwith "Can't write to read-only stream!"
    override __.SetLength(value) = failwith "Can't set length!"


/// Wraps the specified sequence of byte rows in a Stream.
let ofByteRows rows = 
    let flatRows = rows |> Seq.concat
    new ByteEnumeratorStream(flatRows.GetEnumerator())

SeqStreamUse.fs

    let sw = System.Diagnostics.Stopwatch.StartNew()

    let n = 50000
    let bufferSize = 4096
    let lines = Seq.init n (sprintf "line%i\r\n")
    let rows = lines |> Seq.map (System.Text.Encoding.UTF8.GetBytes)    

    let stream = rows |> SeqStream.ofByteRows

    use fs = System.IO.File.OpenWrite(@"c:\users\eulerfx\desktop\test.txt")
    stream.CopyTo(fs, bufferSize)

    sw.Stop()

    printfn "wrote %i rows in %g seconds" n (sw.Elapsed.TotalSeconds)