davidflanagan.com

Method Chaining Part 2

The comments on my last post about method chaining in JavaScript were spectacular, and I want to publicly thank all who took the time to read my code and think about it. The final version of the code (which you can see below the fold) is much stronger thanks to their comments.
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Method chaining in JavaScript inheritance hierarchies

In the 5th edition of my JavaScript book I made the embarrassing mistake of recommending a constructor and method chaining technique that only works for shallow class hierarchies--it works when class B extends A, for example, but not when C extends B and B extends A.

The technique I recommended was to put a superclass property in the prototype object of a class, and then to chain to a superclass constructor by calling this.superclass(). To see why this fails, imagine that we're creating an instance of class C (which extends B which extends A). The constructor C() chains to B() by calling this.superclass(). The constructor method B() is invoked on the same instance of C, however, so when it attempts to chain to A() by calling this.superclass(), it just ends up invoking itself. This incorrect chaining technique is discussed in sections 9.5.1 and 9.5.2, and is also used in example 9-10 and 9-11 at the very end of the chapter. I blogged about this mistake and a possible workaround almost two years ago.

Now, however, O'Reilly is preparing to do a reprint of the book, and I have an opportunity to fix this mistake. Below is a revised code from examples 9-10 and 9-11. I've renamed the defineClass() method to Class() and have modified it so that it automatically does constructor chaining (I was inspired by dojo for this change). More importantly, I've simplified method chaining by defining a global method named chain() for method chaining. If a method overrides a method defined by a superclass (or a "mixin" class) it can invoke that overridden class by invoking chain() like this: chain(this,arguments). (The second argument must be the arguments array of the overriding method, and the first argument must be the object on which that method was invoked.)

The code is below the fold. I think this is interesting JavaScript, and I'd love to have it checked for errors before it goes into print again... Please leave a comment if you think it could be improved! Update: comments are now closed; spammers have struck.
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Ruby Review Roundup

The Ruby Programming Language has been gratifyingly well received by readers and reviewers. In addition to glowing reviews at rubyinside.com and slashdot.org, it has been reviewed ten times at amazon.com and I proud to say that all ten reviews give it a five-star rating.

Here are the reviews. For all except the slashdot review, the linked text is the title of the review:

• The New Most Important Ruby Book [rubyinside.com]
• ...the most authoritative language book for Ruby... [slashdot.org]
• This is the new authoritative Ruby book. Buy it, not the Pickaxe. [amazon.com]
• Finally! And worth it! [amazon.com]
• A Must-Have For Serious Ruby Developers [amazon.com]
• Perfect For Experienced Ruby Developers [amazon.com]
• Great introduction to Ruby for experienced programmers [amazon.com]
• Good book on Ruby [amazon.com]
• The best Ruby book I've seen [amazon.com]
• The Ruby Book! [amazon.com]
• Great! [amazon.com]
• great book [amazon.com]

Thanks everyone!

Errata for my Ruby Book

I've put together a list of 81 errors and updates to my Ruby book. These are fixed in the next printing. If you already own a copy of the book, however, you can go through and enter the changes yourself, if you are so inclined.

I use O'Reilly's style for describing the changes. Each entry in the file begins with a page number within delimiter characters. The delimiters indicate the severity of the change:

• Page numbers in parentheses usually indicate typos or other minor non-technical changes. You can ignore these if you want.
• Page numbers in curly braces indicate minor technical errors that have been corrected
• Page numbers in square braces indicate more severe technical errors that have been corrected. There are only two of these, but they're worth noting.
• Page numbers in angle brackets are updates (this differs a bit from normal O'Reilly style) to keep the book in sync with the evolution of Ruby 1.9. In my opinion, these are the interesting ones.

I've posted my list of changes here. They will all eventually appear on O'Reilly's errata page for the book as well.

Help fix up my book, please

The Ruby Programming Language is going to be reprinted next week, and O'Reilly has given me SVN write access to the docbook files to fix typos, errors, etc. I've got a list of about 25 relatively minor erros that I'll be fixing, but I'd love to stomp out more bugs on this reprint.

So, if you've got a copy of the book, and have found typos, mistakes or omissions, please let me know. You can email me (david@ this domain) or post them as comments on this blog. (Normally, you'd submit them on the O'Reilly website but since time is factor for this reprint, send them directly to me, please.) Keep in mind that this is just a reprint, not a new edition of the book, so I'm pretty constrained about the kinds of changes I can make. I can't add new sections or figures or tables, or cover brand new topics that aren't currently covered. I can often squeeze in short new paragraphs when they're needed to clarify things or if there is something important that I left out.

Thanks to DH, MD, RM, and DB, all of whom submitted one or more errata to me or to O'Reilly's website recently. I don't have access to the names (or initials) of the others who submitted errata to the publisher's website back in March and February.

Update: Thanks to those (BR, CS, ADS, MD) who commented and emailed me with other errors to correct. I ended up making about 80 changes--half to fix typos and minor errors, and half to update the book to track minor (mostly) changes in Ruby 1.9. I'll post a list of all changes soon.

Will C++ get Closures before Java does?

I just read that closures are being added to C++ [PDF link].

A note to Sun: you know your language is falling embarrassingly behind if the C++ standards committee can move more nimbly than you can!

(For those who aren't already sick of reading about closures in Java, Neal Gafter is developing a prototype Java compiler that supports closures, and he even has a JSR proposal drafted and ready to go.)

5 Years in Iraq

Tomorrow marks the 5th anniversary of Bush's war with Iraq. The costs:

• 3990 US soldiers dead That is more than 2 per day.
• 20,416 US soldiers wounded (badly enough to require air transport). That's more than 11 per day.
• At least 82,240 civilians killed. That's 45 a day and only includes deaths that get reported in the media. One study puts the civilian death toll much, much higher.
• $503 billion. That's 275 million dollars a day, and it doesn't include future obligations, such as veteran's health care. (Nobel laureate economist Joseph Stiglitz argues that the war has already cost 3 trillion dollars.)

The blood of 2 soldiers and $275 million down the drain today and tomorrow and the day after.... With no end in sight.

Our elected representatives seem uninterested in stopping this war, but these candidates for the US House of Representatives have a responsible plan to end the war. It is remarkably sane and it is the only glimmer of hope I've had in a long time.

Welcome Slashdot Readers

If you arrived here after reading slashdot's review of The Ruby Programming Language, you've come to the right place. Thanks, Brian, for the kind words! The post below includes links to the book's table of contents and to an interactive preview.