gistfile1.txt

Public NotInheritable Partial Class MoreEnumerable
	Private Sub New()
	End Sub
	<System.Runtime.CompilerServices.Extension> _
	Public Shared Function Batch(Of TSource)(source As IEnumerable(Of TSource), size As Integer) As IEnumerable(Of IEnumerable(Of TSource))
		Return Batch(source, size, Function(x) x)
	End Function

	<System.Runtime.CompilerServices.Extension> _
	Public Shared Function Batch(Of TSource, TResult)(source As IEnumerable(Of TSource), size As Integer, resultSelector As Func(Of IEnumerable(Of TSource), TResult)) As IEnumerable(Of TResult)
		source.ThrowIfNull("source")
		size.ThrowIfNonPositive("size")
		resultSelector.ThrowIfNull("resultSelector")
		Return BatchImpl(source, size, resultSelector)
	End Function

	<System.Runtime.CompilerServices.Extension> _
	Private Shared Function BatchImpl(Of TSource, TResult)(source As IEnumerable(Of TSource), size As Integer, resultSelector As Func(Of IEnumerable(Of TSource), TResult)) As IEnumerable(Of TResult)
		Debug.Assert(source IsNot Nothing)
		Debug.Assert(size > 0)
		Debug.Assert(resultSelector IsNot Nothing)

		Dim bucket As TSource() = Nothing
		Dim count = 0

		For Each item As var In source
			If bucket Is Nothing Then
				bucket = New TSource(size - 1) {}
			End If

			bucket(System.Math.Max(System.Threading.Interlocked.Increment(count),count - 1)) = item

			' The bucket is fully buffered before it's yielded
			If count <> size Then
				Continue For
			End If

			' Select is necessary so bucket contents are streamed too
			yield Return resultSelector(bucket.[Select](Function(x) x))

			bucket = Nothing
			count = 0
		Next

		' Return the last bucket with all remaining elements
		If bucket IsNot Nothing AndAlso count > 0 Then
			yield Return resultSelector(bucket.Take(count))
		End If
	End Function
End Class

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