Primitive streams

[Raab, Donald]

We thought it would be worthwhile for GSC.  

Here's an example usage from our Kata in the Order class, getValue() method:

	return this.lineItems.sumOfDouble(LineItem::getValue);  

vs. 

	return this.lineItems.stream().map(LineItem::getValue).reduce(0.0, (x, y) -> x + y);

The second one does require more awareness and understanding.  I understand the second one, but I would use the first one if I needed a sum and it was available on the API.  

I assume sum would look like this on streams if/when you add the Double version of stream:

	return this.lineItems.stream().map(LineItem::getValue).sum();

and the short-hand would look as follows:

	return this.lineItems.stream().sumBy(LineItem::getValue);

The short-hand version might be easier to discover in the IDE.  Eventually, Java developers will wade into the deeper end of the pool with map and reduce.  

> > While many Java programmers are unfamiliar with reduce, there are many
> > FP-aware folks (ruby, groovy, etc) who will want to transfer their
> > favorite expressions to Java. We shouldn't go out of or way to make
> > this transfer difficult.
> 
> No, we're not going to make this difficult.  Those already familiar with
> reduce should be pretty happy.
> 
> The question is, what should we do to accomodate the other 95% of java
> developers?  Giving them reduce *only* seems like throwing them in the deep
> end of the pool.
>