Add Predicate.of(), Consumer.of(), etc.

Paul Sandoz paul.sandoz at
Wed May 6 10:37:34 UTC 2015

On May 2, 2015, at 11:31 PM, Remi Forax <forax at> wrote:

> Hi all,
> today, I stubble on a variant of JDK-8050818 [1],
> trying to call negate() on a lambda which is not yet a Predicate (due to target typing) which requires either to cast the lambda to a Predicate and everybody knows that cast are evil or to add a local variable.
> I think there is a way to fix that, it's not very orthodox so I let you judge.
> The idea is to introduce a static method 'of' on Predicate,
>  class Predicate<T> {
>    ...
>    public static <T> Predicate<T> of(Predicate<T> predicate) {
>      return predicate;
>    }
>  }
> so one can write:
>  stream.filter(Predicate.of(String::isEmpty).negate())
> compared to
>  stream.filter(((Predicate<String>)String::isEmpty).negate())
> so the question is, does it it worth the cost to introduce a static method that basically do nothing on all functional interfaces of java.util.function.

That does have the virtue of not adding a static method per operation but i still cannot bring myself to add such methods as a work around for seems like a compiler inference problem (albeit one in which might be very tricky or not possible to solve).

In some respects i wonder if the default methods on the functional interfaces are an attractive nuisance.


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