I maintain a utility library for Dart called Quiver, that you could view in the same vein as Underscore, or Guava. Like you mention, the Dart core libraries are

I maintain a utility library for Dart called Quiver, that you could view in the same vein as Underscore, or Guava. Like you mention, the Dart core libraries are pretty rich, so Quiver doesn't have to define as many fundamental concepts. But rather than there being a sprawling library, many of the nice things come about from composing a couple of features. My favorite example is Iterable. Dart's Iterable interface doesn't just have .iterator, it has .forEach(), .map(), .where(), .reduce(), .take(), .first, .last... 27 methods and getters! This makes using Iterables a consistent pleasure, but it could be a heavy burden on Iterable implementors, except that Dart has mixins and the IterableMixin, so all you need to do to implement the 27 methods is implement .iterator and use the mixin, which uses .iterator to implement everything else. The ubiquity of Futures and Streams and how dart:html uses them consistently instead of raw callbacks is another example. There are other Iterable utilities that are possible, which is where one of Quiver's libraries steps in to provide things like zip(), enumerate() and partition(), which does raise the same question you ask: why are the built-ins special, where do you draw the line? That's a judgement call where I tend to fall on a pretty pragmatic side of things. Programmers benefit from consistency - not just because there's one way to learn how to do things, but also because some powerful idioms, like more functional-style programming, become popular in a vicious cycle: as they become more common, more people learn them and they become even more common. Having some of the higher-level bits ship with the platform makes everyone's life easier. quiver: http://pub.dartlang.org/packages/quiver http://pub.dartlang.org/packages/quiver