Provides a secondary source that will be consumed if this source completes without any elements passing by. As soon as the first element comes through this stream, the alternative will be cancelled. It is recommended to use the internally optimized LeftTLeft, TRight(TLeft, TRight) and RightTLeft, TRight(TLeft, TRight) combiners where appropriate instead of manually writing functions that pass through one of the values.

public static Source<T, TMat3> OrElseMaterialized<T, TMat, TMat2, TMat3>(
	this Source<T, TMat> flow,
	IGraph<SourceShape<T>, TMat2> secondary,
	Func<TMat, TMat2, TMat3> materializedFunction
)

[<ExtensionAttribute>]
static member OrElseMaterialized : 
        flow : Source<'T, 'TMat> * 
        secondary : IGraph<SourceShape<'T>, 'TMat2> * 
        materializedFunction : Func<'TMat, 'TMat2, 'TMat3> -> Source<'T, 'TMat3>