[akeefer]

I have to respectfully disagree. First of all, the things he shows aren't inherently complex: adding an additional function to the existing collections library is something that's possible in other languages in less confusing ways (see other examples in this post). The various concepts required to solve the problem in Scala like implicits and higher kinds might be inherently complex, but the problem he's trying to solve isn't inherently complex. And while the Scala solution might not be 100% identical to, say, just adding the method directly to a class in Ruby (since in Scala it's type-safe, etc. etc.) that's still missing the point. The point is that if you sit down and say "I want to add a method to all my collections that works like the existing methods," in Scala it requires an understanding of a huge number of complicated intersecting concepts, whereas in other languages it doesn't.

Secondly, excusing complexity by saying "it makes things possible that wouldn't otherwise be possible" isn't really enough of a justification. The question is: do those exact things need to be possible? Or is there some way that gets me 90% of the way there without the complexity, and that's good enough? More power isn't always better, which was a big part of the point of the article. Just dismissing it by saying "well, the complexity lets you do powerful things" doesn't really refute the point of the article, it totally misses it.

There's a tradeoff to be made. You might make those tradeoffs differently than I would, which is totally understandable, but we should at least be able to have a conversation about the fact that there is such a tradeoff without people dimissing statements like "Scala is complex" out-of-hand.

[harryh]

"adding an additional function to the existing collections library is something that's possible in other languages"

Is it possible in other statically compiled strongly typed languages? I don't think so?

The advantages/disadvantages of static vs. dynamic languages seem out of scope for the "is scala too complex?" question.

[akeefer]

See my examples below for how to do it in Gosu (via enhancements). In C# it's pretty much the same (via extension methods). Both are statically typed languages. Again, not 100% the same as Scala, and each comes with a different set of tradeoffs than the Scala approach (i.e. they're statically dispatched in Gosu), but they're certainly both reasonable, and much "simpler", solutions to the problem of "how do I add a filterMap function to all arrays or collections that works pretty much how I want it to."

[harryh]

OK I read up some on this and neither Gosu enhancement nor C# extended methods come close to what the post author is trying to attempt (adding methods to Seq and having them automatically get attached to Array, String, and CharSequence) with a single method.

So it doesn't really seem like they solve the problem "how do I add a filterMap function to all arrays or collections that works pretty much how I want it to" any simpler than Scala. All the complexity that the author brings up in his post is because he was trying to add this functionality with a single method (and a bunch of implicits).

[Dn_Ab]

Up top http://news.ycombinator.com/item?id=3444688 I gave working code that comes close. To be fair the reason why it gets closer (works with both F# and C# lists,arrays, sequences,dictionaries,maps,strings etc) is clerical. From this thread, I understand Scala and Java arrays are divorced.

But the problem is: put in a string and it gives back a list of characters. So I use the term it is "topologically correct" heh. To be honest I do not think there is anything functional about what he is attempting but perhaps the idioms in Scala are different? My knowledge of scala is mostly horizontal (from Ocaml,F#, haskell).

[soc88]

Returning the most precise result types (both collection _and_ element type) is a requirement. If this wouldn't be required, the problem would be much easier.

[harryh]

Very interesting. I'm gonna go read more about this stuff now. Thanks!

[soc88]

You pretty much point to solutions which don't solve the problem mentioned in the blog post at all and seeing how C# extension methods basically reintroduced instanceOf checks as an implementation necessity I'm pretty sure that extension methods are the wrong way to go.

[rwallace]

I don't remember C# extension methods being particularly prone to incur instanceOf checks, but I could be missing something; can you expand on this?

[soc88]

Have a look at how stuff like Count is implemented. It basically does instanceOf checks for ICollection to figure out if the underlying type supports a better way to compute the result (instead of iterating trough the whole collection).

This is completely non-extensible and people have to pay the price for this syntactic sugar (e. g. extension methods not discoverable with Reflection).

Other languages have a much cleaner approach: traits (in languages like Scala) and default methods (in Java) both solve the problem in a more straightforward and correct way.

[chollida1]

> Is it possible in other statically compiled strongly typed languages? I don't think so?

Sure it is :) see C# http://msdn.microsoft.com/en-us/library/bb383977.aspx

[soc88]

I don't see how it solves the problem mentioned.

[michaelochurch]

First of all, the things he shows aren't inherently complex: adding an additional function to the existing collections library is something that's possible in other languages in less confusing ways (see other examples in this post).

It's very easy to write a new function for your particular case. You can write an acceptable map function for your new collection, or a new list-munching function, just as easily as in ML. It will be a top-level function instead of a method, but that's usually just fine (if inelegant).

The long-term risk you are taking is that you might want this list-munching function to apply to other collection types and will now have code duplication.

What Scala offers is the ability to write new methods that apply to all collections (Strings, BitSets, Lists) if you wish... and to create new collections types (with a little bit of work and comprehension, but not as much work as is involved in writing 50+ library functions by hand) that automagically end up with all the collections functions.

This impressive and quite radical code reuse is the part that's hard about Scala, but that's only relevant if you want to write libraries at the L2/L3 level of quality and beauty.

[akeefer]

But again, other languages do offer the ability to write methods that apply to all collections, without the "complexity." Sure, it's different, but in Gosu for example you can write an enhancement method on the Collection interface, or on the List interface, and now everything that implements Collection or List has that method. It's then a matter of whether or not the objects in question implement that appropriate interface or not. Your new functions apply to everything that implements those interfaces, and if you want a new thing to have all those methods then you just implement the interface and you get all 50+ functions for free.

Scala offers a particular way to solve that problem that has its own plusses and minuses, but it's not the only way for a language to let you do that, and it's certainly not the "simplest" way to accomplish that goal.

[modersky]

Arrays are not collections, either in Scala, or in the blog's condensation of it. But the blog nevertheless tries to define a single extension method that works for both sequences and arrays. I do not think this problem has a simple solution in any language.

[akeefer]

That's a fair point; there's no simple way that I know of to do that in any language (though many languages avoid having both constructs), and the general solution is to write parallel sets of methods to operate on the two types of data structures.

[soc88]

> First of all, the things he shows aren't inherently complex: adding an additional function to the existing collections library is something that's possible in other languages in less confusing ways

> "I want to add a method to all my collections that works like the existing methods," in Scala it requires an understanding of a huge number of complicated intersecting concepts, whereas in other languages it doesn't.

Sorry, but there is a bit more to it. I will gladly accept a link to a language which does all the stuff he was trying to do, but until then I'm not convinced at all.