CSCI E-168

See p. 71 of the PDF, and type these into irb:

{ dog: 'canine' }
{ :dog => 'canine' }

I think the point is that in the colon syntax, the key must observe the naming conventions for symbols (start with a letter, etc.). I.e., the name would be appropriate for a symbol. Further, there is no way to embed a space (or non-alphanumeric chars) into the key name.

A student asked: Why, when two objects are instantiated in a row, did the object_id skip a number?

Answer:

Live and learn. The Matz Ruby Interpreter (MRI) reserves odd object_id's for Fixnums. So try this in irb:

0.object_id
1.object_id
2.object_id

etc.

If you do

Object.new.object_id
Object.new.object_id
etc.

you will see that the id's are allocated in a different range.

JRuby -- which is what is used in the slides -- observes the MRI convention for Fixnum's, but allocates new object at the smallest object_id available.

The backdrop for this is that while Fixnum's behave like objects, they are represented internally as immediate values, and the object_id is a "function" of the value.

For some interesting discussion around this, see http://groups.google.com/group/ruby-talk-google/browse_thread/thread/2de0fb648d328ce9/83f16316f51904e6?show_docid=83f16316f51904e6

@Gabriel

Yes: create a file in your login directory called .irbrc (you can leave out the dot if you like).

Then put this in there:

def ri(*names)
system(%{ri #{names.map {|name| name.to_s}.join(" ")}})
end

Save the file, and then type from within irb:

ri "String#reverse"

(You will need the quotation marks if there is a syntactically important bit of Ruby -- such as the # -- in the request.)

There are fancier ways to do this so you don't leverage the "system" call, but I think this is good enough for now.

This used to be in the Pickaxe, but I can't find it in the new edition.

@Ron Newman

Interesting. After my setup, there is no .irbrc.

To learn about IRB.conf, take a look at chapter 18 in the Pickaxe.

@Virginia

I just started the video and it worked for me.

There is a phone number for technical support: 617-998-8571.

I believe students are allowed/encouraged to call this number: If you do, post any results here.