Comment by michaelochurch | Hacker News Reader

Comment by michaelochurch | Hacker News Reader

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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.

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.

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.

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.

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