OOPSLA Day 2: More on Dart

I think when people saw that Dart was from Gilad Bracha and Lars Bak there was an expectation that Dart was going to be a grand synthesis: a blazingly-fast NewSpeak-with-curly-brackets. It’s very much not such a language. It doesn’t seem, academically, vastly innovative because it doesn’t add much. But, in truth, optional types are a radical design decision in that they take away runtime aspects that a lot of mainstream programmers expect. (Of course, this raises the question of how to define the “mainstream”…)

Pros and Cons of Mandatory Typing In Descending Order of Importance (per Gilad Bracha):


  • machine-checkable documentation
  • types provide conceptual framework
  • early error detection
  • performance advantages


  • expressiveness curtailed
  • imposes workflow
  • brittleness

Having said that, I attended a lecture in which someone, perhaps from Adobe, measured the performance impact of optional typing. Their conclusion, although admittedly done on the troublesome-ly small and artificial SunSpider benchmarks, was that the performance penalty of implicit types amounts to 40% (with a very large standard of deviation). That “feels” about right to me — definitely significant but not the overwhelming performance benefit you might get from either parallelization or an algorithmic change.