[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.