Nominal typing or structural typing?

[Brian Goetz]

> I'm worried about lambdas effect on the generation of classfiles
>
> First, that they aren't held in a separate class file, because that is one
> of the reasons anonymous classes are frowned for more performance sensitive
> areas.

Lambda expressions create no side-file artifacts.

> Second, that they reuse definitions with the same number and type of
> arguments - structural typing - i don't really just want to replace
> anonymous class runtime explosion with the lambda equivalent, but have
> something better.

No, we are not introducing structural function types to Java at this 
time.  This idea has been rejected after extensive exploration, largely 
because *erased* function types would be terrible.

What we do re-use is applicable interfaces of the "right shape", of 
which many already exist (Runnable, Comparator, etc.)  This is what Java 
developers have done since day 1 -- model functions as interfaces with 
one method, and we piggyback on that approach.  We introduce no new 
kinds of types to the type system; instead, lambda expression become a 
way to create instances of types like Runnable and Comparator.