`bool Function(...)` tear-off could accept the `!` operator in front

[FMorschel]

I've recently run into a project where I had a list of objects and wanted to test and process them using the Iterable.*where* / Iterable.*when* / Iterable.*while* methods. So I've created a function where it received a bool Function(MyClass element) test parameter.

In some places, I would use the positive results of this test, so I could easily do iterable.*where*(test) but in other places I would use the negative results, so I would need to write iterable.*where*((e) => !test(e)).

This made me wonder whether iterable.*where*(!test) should exist.

[mraleph]

As an option (if you really find yourself writing this code a lot) you could just use higher order function:

bool Function(E) not<E>(bool Function(E) predicate) {
  return (e) => !predicate(e);
}

iterable.where(not(test));

[lrhn]

Or

extension NegFunc<P> on bool Function(P) {
  bool Function(P) get not => (P value) => !this(value);
}

so you can do:

iterable.where(test.not)

I actually think whereNot should be a method on Iterable. We failed to add it for Dart 2.0, and we're unlikely to change the interface now, so we instead added it as an extension method instead, in package:collection.

There is no corresponding takeWhileNot/skipWhileNot. There probably could be.

[FMorschel]

Or

extension NegFunc<P> on bool Function(P) {
  bool Function(P) get not => (P value) => !this(value);
}

so you can do:

iterable.where(test.not)

I like the idea but the reading is a bit odd compared to iterable.where(not(test)); imo.

I actually think whereNot should be a method on Iterable. We failed to add it for Dart 2.0, and we're unlikely to change the interface now, so we instead added it as an extension method instead, in package:collection.

There is no corresponding takeWhileNot/skipWhileNot. There probably could be.

I really like this option, I think I'm going to be using this.