On Thu, Nov 24, 2011 at 1:28 AM, Kevin Wright <kev.lee.wri...@gmail.com>wrote:
>
> This is all 100% safe and statically typed, and is made possible by the
> "scary" CanBuildFrom implicit parameter that Stephen mention in his article.
>
> I don't believe that Fantom can do this
>
It depends on what you mean by "this", but the answer is that Fantom
certainly can (as can all these other languages I'm sure). I'm providing
the code below and not here since I don't want to turn this into a Scala
vs/ Fantom debate, which is not the point I'm trying to make here. In this
particular example, you're just morphing one map into another, which is
really trivial. Admittedly, Fantom requires to declare a new map and then
adding the new content to that map, but you will probably do that in Scala
as well if you want to reuse that result (which I bet you would in a real
program and not a code golf).
> , not least because it doesn't have highly-optimised collection types such
> as BitSet
>
Maybe, maybe not. Optimized libraries are a separate topic from language
comparisons.
The bottom line here, again, is that implicit CanBuildFroms and other
subtleties are a very specific implementation detail in Scala that are not
necessary for languages that followed a different path to build their type
system.
By the way, I don't think the Liskov Substitution Principle is applicable
here since a function taking a Map[Int,String] will certainly not be happy
if you pass it a Map[String,String].
> , it doesn't consider Maps to subclass collections of pairs
>
True, but this seems is a collection design choice, not a language feature
(I like it, personally).
> , and it doesn't support creation of your own paramaterised collection
> types. So far as I'm aware, Scala is the only language in existence that
> directly supports such a scheme (though I imagine it would be totally
> possible to duplicate using something like Lisp macros)
>
I don't think so but if I misunderstood your point, feel free to clarify.
Finally, the code to morph the map:
aMap := [1:"x", 2:"y", 3:"z"]
// Create an empty map
map2 := [:]
// Create the map ["1":"x", "2":"y", "3":"y"]
aMap.each |v,k| { map2[k.toStr] = v }
// map2 is now a [Str:Str]
echo(map2)
--
Cédric
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