London Lambdas Hackday: Existing Code

[Brian Goetz]

>>> People using Guava's predicate library already will have an interface
>>> doing something identical to the Java 8 Predicate.  Furthermore they
>>> will be able to
>>
>> to?
>
> hmm, apologies, let's back this sentence up a bit:
>
> Furthermore they already have a large body of predicate instances that
> exist within the guava space.  Or that they may be using within their
> own code.  These won't be usable with Java 8 predicates because they
> are of a different nominal type.
>
> The only way I could think of addressing this issue was allowing
> implicit type conversions at target typed locations between functional
> interfaces if they have the same structural type.  So you'd be able to
> write:
>
>   java.util.functions.Predicate<?> TT =
> com.google.common.base.Predicates.alwaysTrue();

We considered this but a conversion from one type to another just 
because they are structurally similar (and we have no reason to believe 
either came from a lambda) was too much.  However, there's a simpler route:

   LegacyPredicate p = ...
   Predicate pp = p::isTrue;

This lets us scoop out the functionality the same conversion that is 
already present, rather than introducing a new one.