Bools and explicitness [was Re: PyWart: The problem with "print"]

[Robert Kern]

On 2013-06-06 10:45, Chris Angelico wrote:

> For the "accept any object that has a next() method" sorts of rules, I
> don't know of any really viable system that does that usefully. The
> concept of implementing interfaces in Java comes close, but the class
> author has to declare that it's implementing some named interface. In
> theory there could be something that deduces the validity from the
> given structure, but I'm not aware of any language that does this. But
> it would let you do stuff like this (prototyped in Python):
>
> class Integers:
>      def __init__(self): self.value=0
>      def next(self):
>          self.value+=1
>          return self.value
>
> interface Iterable:
>      next(self)
>
> def grab_three_values(Iterable iter):
>      return iter.next(),iter.next(),iter.next()
>
> With a language that checks these sorts of things at compile time,
> it's not a big deal to test. With something fully dynamic like Python,
> it's probably not worth the effort. But maybe checks like this could
> be useful to something like Coverity.

As Serhiy notes, Go does this, almost exactly as you wrote it (modulo syntax).

http://golang.org/doc/effective_go.html#interfaces_and_types

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
  that is made terrible by our own mad attempt to interpret it as though it had
  an underlying truth."
   -- Umberto Eco