Updated State of the Lambda

[Brian Goetz]

Yes, this is well-covered ground.  What you're asking for is "function 
types" (or arrow types, or algebraic function types, or structural 
functions types.)  The short answer is "no".

Function types are the "obvious right way" to represent the type of a 
lambda, until you realize that they will end up getting implemented 
using generics, which means they will be erased.  Erased function types 
are the worst of both worlds.

Instead, we use functional interfaces in APIs, and then users can use 
named classes, anonymous classes, or lambdas to create instances of the 
functional interfaces.


On 12/9/2011 1:44 PM, Yuval Shavit wrote:
> By the way -- and I apologize if this has already been covered, I did
> some searching and nothing came up -- is there any thought as to whether
> methods will ever be able to declare lambdas as arguments?  Something like:
>
>     public <T> void myFilter(Iterable<? extends T>, (? super T ->
>     boolean) predicate ) { ... }
>
>
> This function could then take either a lambda of the same type, or any
> reference typed as a functional interface which could be expressed as a
> corresponding lambda.
>
> Thanks,
> Yuval
>
> On Fri, Dec 9, 2011 at 1:28 PM, Brian Goetz <brian.goetz at oracle.com
> <mailto:brian.goetz at oracle.com>> wrote:
>
>     An updated State of the Lambda is available here:
>
>     http://cr.openjdk.java.net/~briangoetz/lambda/lambda-state-4.html
>
>
>