Summarising lambda features

[Brian Goetz]

Just some quick comments.

I would write this example:

Iterable<String> names = Arrays.asList("Alice", "Bob", "Charlie", "Dave");
Iterable<String> filteredNames = names
         .filter(e -> e.length() >= 4)
         .into(new ArrayList<String>());
for (String name : filteredNames) {
     System.out.println(name);
}

instead as

List<String> filteredNames = names.filter(...).into(...);

The whole point of into() is to put the data into a *collection*, where 
you can process it outside of the streams library.  If all you wanted 
was an Iterable, you could drop the into() stage.

As a general rule, if Iterable appears in the client code, someone 
probably made a mistake.

Note also the APIs for stream operations (filter/map/forEach) are going 
to change (returning a Stream abstraction, which will be more like an 
Iterator than an Iterable), whereas the client code invocations for 
using them will not.  So that's two reasons to not use Iterable in these 
examples.

I would change "Elements are computed lazily" to "Elements *may be* 
computed lazily", as the next round defers the choice of lazy/eager 
until it sees the end of the pipeline, and knows whether you are 
consuming the whole stream or not.  If so, there are more efficient 
means of traversal than iterators.

Internal iteration doesn't just hide implementation decisions; it gives 
implementations flexibility to use laziness, out-of-order, parallelism, 
or whatever other trick it deems effective.

Method references are a bigger deal than your examples suggest.  There 
are lots of mappers/predicates/sinks that are already represented as 
methods:

   strings.map(String::length).forEach(numbers::add);

(Where "strings" and "numbers" are collections.)

On 6/22/2012 7:49 PM, James Shaw wrote:
> Having lurked on this list for a while, after reading Brian Goetz's State
> of the Lambda articles, and having struggled with javac myself over several
> evenings, I've had a stab at summarizing the new features available in the
> lambda binary build.
>
> http://datumedge.blogspot.co.uk/2012/06/java-8-lambdas.html
>
> I hope some folks find this useful.  I've tried to be as accurate as I can
> within the limitations of my knowledge; if there are glaring mistakes, do
> tell me ;-)
>