tee()

[Tim Peierls]

On Thu, Jan 24, 2013 at 3:43 PM, Kevin Bourrillion <kevinb at google.com>wrote:

> It just feels very, very strange to let the user inject a side-effect into
> the middle of their stream somewhere, for mysterious hidden later execution
> *maybe*.
>

If tee stays in -- not saying it should -- what about a special argument
type:

    <T> Stream<T> tee(Observer<? super T> observer);  // tee ->
observingWith ?

where

    public interface Observer<T> /* does not extend Consumer/Sink/Block! */
{
        void observe(T value);
    }

That distinction would be lost when using lambdas, but in other cases it
could serve as a reminder that you can look but not touch.

Maybe have a boolean return from observe, with false meaning "no longer
interested in observing". That would prevent lambda writers from
accidentally using something that looks like a Consumer/Sink/Block.

--tim
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