Re: AbstractTraversable.headOption throws NoSuchElementException

On Wed, May 06, 2015 at 12:58:06PM -0700, Rex Kerr wrote:
> I'm not sure there's any way to catch wonky usages of the API except to try
> them and see what happens (and submit a bug report to the offending project
> if it does something weird).

This might be overkill for Scala collections, but I could imagine
publishing a laws package that encodes the invariants for each
collection type, allowing folks to easily test their own custom
implementations against the expectations of the API/library.

For example, I could imagine testing the following properties:

    // C[A] <: Iterable[A]
    forAll { (xs: C[A]) =>
      val lst1 = xs.iterator.toList
      val lst2 = xs.iterator.toList
      lst1 shouldBe lst2

      xs.size shouldBe xs.iterator.size

      xs.isEmpty shouldBe xs.iterator.isEmpty

      // ...and so on
    }

I just thought I'd mention this, since the strategy of exporting laws
to test against has been pretty successful in the "functional" corner
of the Scala ecosystem.

-- Erik

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