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Comment by laureny | Hacker News Reader

> I think that all the metaprogramming magic that Ruby allows is at odds with speed.

I don't think so, Java and C# also have metaprogramming (reflection, class loading, bytecode manipulation) and they are still plenty fast.

Ruby's liability is that it's dynamically typed, and this puts a hard limit on how fast it can be (and also on how toolable it can be, but that's a separate discussion).

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Reflection in Java is in fact slow. The difference is that in ruby that stuff is pervasive, in Java you rarely use reflection.

Reflection is also very slow in C#

Not it is not. A lot of basic metadata is cached and quickly accessible.

How much metaprogramming is normally going on behind the scenes in a typical Ruby/Rails app vs Java or C# though?

If you do a lot of reflection in Java then you'll end up with some pretty crummy performance, but the average Java program doesn't have much.

It's not just the actual metaprogramming, i.e. define_method is slow. It's also the runtime implications of metaprogramming being possible, i.e. needing to dispatch each and every method call dynamically just in case someone called define_method. Java can turn every method call into a function pointer at compile time.

Metaprogramming is code using define_method (optionally closing over local variables), instance_eval, and stuff of that nature. Even with bytecode manipulation they would be very difficult to emulate in Java/C++ and would be quite slow.

That said, JavaScript is not far off of Ruby's monkeying capabilities and yet pretty darned fast.

I mean metaprogramming support is kind of a spectrum and neither Java nor C# support it to the same degree as Ruby. For one thing and for another, C# and Java have large corporations supporting those languages which try very hard to make the runtimes fast so it's not a fair comparison.

Then compare it with compilers for dynamic languages like Lisp, Scheme, Dylan, Smalltalk...

I said tricky, not impossible but I will, even though I'm not sure I'm really qualified to talk about these languages for one thing and for another, I think that these sort of comparisons are pretty pointless to begin with. Also I'm not sure where you are exactly going with your comment.

Lisp + Scheme: I mean if nothing else, people have been trying to make them fast for the last more than half of century. Plus AFAIK most Lisp meta-programming code is generated during compile time through macros not during run-time.

Dylan: I don't really know anything about Dylan but it seems to have come out of Apple and CMU, so there's that. Plus it seems to be just a Lisp dialect.

Smalltalk: You consider Smalltalk fast? Lol.

>Smalltalk: You consider Smalltalk fast? Lol.

Well, any Smalltalk JIT beat the standard Ruby implementation hands down, what can I say?!

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