Feeds

Converting Groovy to Ruby

A different spin on Java

Security for virtualized datacentres

In this post, Glen Stampoultzis posts a very interesting and clever sequence of steps by which he converts a piece of Java code into idiomatic Groovy code. I thought it was a nice article, so I'll do a very short spin on it: taking Glen's final Groovy code and converting it into idiomatic Ruby.

(I'll probably get my pants flamed off by you-know-who, but hey, it's a slow Thursday afternoon).

Glen's code, an algorithm for finding all n-length subsequences in a given array, ends up here:

def subn(n, list) {
    if (n == 0) return [[]];
    if (list.isEmpty()) return [];

    def remainder = list.subList(1, list.size());
    return subn(n-1, remainder).collect() { [list.get(0)] + it } + subn(n, remainder);
}

(I had to make some edits because his code didn't appear to format right; I don't claim this code is 100 per cent correct in this state).

Admittedly it's a very nice reduction from the original Java code. As Glen correctly surmises, it's largely due to those super-nice closures we get from Groovy. My first step is to make a few minor changes to make it run correctly in Ruby:

def subn(n, list)
    return [[]] if (n == 0);
    return [] if (list.empty?());

    remainder = list.slice(1, list.size());
    return subn(n-1, remainder).collect() {|it| [list.at(0)] + it } + subn(n, remainder);
end

The most notable changes here are flopping the statement-modifying conditionals on the first two returns and adding an "it" parameter to the collect block. Oh, there's also the "empty?" method. But largely it looks like pretty much the same code. The next obvious step is to remove things that aren't needed in Ruby.

def subn(n, list)
    return [[]] if n == 0
    return [] if list.empty?

    remainder = list.slice(1, list.size)
    return subn(n-1, remainder).collect {|it| [list.at(0)] + it } + subn(n, remainder)
end

Mostly just removing some parens that are unnecessary (and distracting, for me) as well as line-terminating semicolons. Note that Groovy also can omit line-terminating semicolons. I think it's a matter of taste.

def subn(n, list)
    return [[]] if n == 0
    return [] if list.empty?

    remainder = list[1..-1]
    subn(n-1, remainder).collect {|it| [list[0]] + it } + subn(n, remainder)
end

Now we've eliminated the last "return" statement and made the list accesses use the array-referencing "[]" method... in the first case with a more idiomatic range of values rather than two parameters. Again, a matter of taste I suppose; two arguments works just fine. So that brings us mostly to the end of converting from the original Groovy code into Ruby. The new version is as readable as the original, but shorter by several characters. And of course this is my biased opinion, but it reads nicer too. I'm sure that will bring about all sorts of flaming in itself.

At any rate, my point in this is certainly not to start a flame war about which version is better. My point is that the Groovy and Ruby versions are still largely the same. If you can learn to produce the Groovy end result, you can just as easily learn to produce the Ruby end result. So if you've stuck with Java because you're worried you can't learn Ruby, or you don't think Ruby is enough like Java... don't be scared! A whole Rubylicious world awaits you.

Oh, and for you Rubyists out there... feel free to post your own improvements in the comments. I didn't want to change the original flow of the code, but I know it can be golfed down a lot more.

Originally published at Charles Nutter’s blog Headius. A Java developer since 1996, JRuby project-lead Charles joined Sun Microsystems in 2006.

Intelligent flash storage arrays

More from The Register

next story
Microsoft to bake Skype into IE, without plugins
Redmond thinks the Object Real-Time Communications API for WebRTC is ready to roll
Microsoft promises Windows 10 will mean two-factor auth for all
Sneak peek at security features Redmond's baking into new OS
PEAK APPLE: iOS 8 is least popular Cupertino mobile OS in all of HUMAN HISTORY
'Nerd release' finally staggers past 50 per cent adoption
Mozilla: Spidermonkey ATE Apple's JavaScriptCore, THRASHED Google V8
Moz man claims the win on rivals' own benchmarks
FTDI yanks chip-bricking driver from Windows Update, vows to fight on
Next driver to battle fake chips with 'non-invasive' methods
DEATH by PowerPoint: Microsoft warns of 0-day attack hidden in slides
Might put out patch in update, might chuck it out sooner
Ubuntu 14.10 tries pulling a Steve Ballmer on cloudy offerings
Oi, Windows, centOS and openSUSE – behave, we're all friends here
Was ist das? Eine neue Suse Linux Enterprise? Ausgezeichnet!
Version 12 first major-number Suse release since 2009
prev story

Whitepapers

Why and how to choose the right cloud vendor
The benefits of cloud-based storage in your processes. Eliminate onsite, disk-based backup and archiving in favor of cloud-based data protection.
Getting started with customer-focused identity management
Learn why identity is a fundamental requirement to digital growth, and how without it there is no way to identify and engage customers in a meaningful way.
High Performance for All
While HPC is not new, it has traditionally been seen as a specialist area – is it now geared up to meet more mainstream requirements?
Saudi Petroleum chooses Tegile storage solution
A storage solution that addresses company growth and performance for business-critical applications of caseware archive and search along with other key operational systems.
Protecting against web application threats using SSL
SSL encryption can protect server‐to‐server communications, client devices, cloud resources, and other endpoints in order to help prevent the risk of data loss and losing customer trust.