Code explanation requeted

Ruby
1

Hi, Can someone please shed some light on the following code:

def test_listen
s = nil
log = Object.new
class << log; self end.send(:define_method, :to_int) {
s.close
2
}
inet_stream do |s|
assert_raise(IOError) {
s.listen(log)
}
end
end

In particular the “class” statement and “self
end.send(:define_method, :to_int)”

Is this actually a class and where is its “end”?

I didn’t know you can have a class inside a method. So I’m confused here
as well.

This code is messing up the Ruby parser I’m working on in my IDE.

Neville F., http://www.getsoft.com http://www.surfulater.com

2

Hi –

On Tue, 6 Feb 2007, Neville F. wrote:

inet_stream do |s|
Is this actually a class and where is its “end”?
It is a class; it’s the singleton class of log. You may join the club
of people who want a singleton_class method :slight_smile: That would make it:

log.singleton_class.send(:define_method, :to_int) …

As it stands, in order to address the singleton class as an object,
you have to capture it through the technique of:

class << log
self
end

What you’re seeing in the code you’ve got is this, but strung together
on one line without much to help you parse it visually if you don’t
already know what to expect. I would tend to write it as:

(class << log; self; end).send etc.

David

3

unknown wrote:

…
What you’re seeing in the code you’ve got is this, but strung together
on one line without much to help you parse it visually if you don’t
already know what to expect. I would tend to write it as:

(class << log; self; end).send etc.

David

Thanks David. And there I was thinking us C++ folks were good at writing
incomprehsible code. :slight_smile:

Neville F., http://www.getsoft.com http://www.surfulater.com

4

On Tuesday 06 February 2007 04:15, Neville F. wrote:

(class << log; self; end).send etc.

Thanks David. And there I was thinking us C++ folks were good at writing
incomprehsible code. :slight_smile:

:slight_smile: i know it may sound overkill, but if you really want to understand
what the
heck these singleton/eigen classes are, this one is for you:

http://rhg.rubyforge.org/chapter04.html

but maybe you should also read the previous chapters as well, it
shouldn’t
take more than some hours to have the big picture clear in your mind.

the documentation is based upon ruby 1.7.3, IIRC, and I don’t know
what’s
changed later, but I’m sure that the overall cleanness of MRI hasn’t
been
altered :).

def post_scriptum; puts yield end
post_scriptum do %{
hello list! this is my first post!
lurking from some months, I learned a lot from you all!
thanks!
} end

5

On Feb 5, 2007, at 6:39 PM, [email protected] wrote:

What you’re seeing in the code you’ve got is this, but strung together
on one line without much to help you parse it visually if you don’t
already know what to expect. I would tend to write it as:

(class << log; self; end).send etc.

I’d add that

send(:define_method, :to_int)

is used instead of simply:

define_method(:to_int)

to override the private status of ‘define_method’.

Gary W.