Basic Syntax for Extending Instances

ruby-talk
1

Thank you!

I’ll have to do a little re-reading to understand this fully; so, your
version adds an “instance instance variable” (as opposed to a “class
instance” variable)?

Thank again!

Matt

···

-----Original Message-----
From: Austin Ziegler [mailto:austin@halostatue.ca]
Sent: Monday, January 05, 2004 2:54 PM
To: ruby-talk@ruby-lang.org
Subject: Re: Basic Syntax for Extending Instances

On Tue, 6 Jan 2004 04:42:26 +0900, Lipper, Matthew wrote:

Hey everybody,
Given the following extension to the Date class:
class Date
attr_accessor :date_precision
class << self
alias_method :old_civil, :civil
def civil(*args)
# How to make this visible?
@date_precision = args.shift
puts “#{@date_precision}” if($VERBOSE) # >> DAY_OF_MONTH
return old_civil(*args)
end
end
end

date = Date.civil(“DAY_OF_MONTH”,2004,2,5)

#Doh!
puts date.date_precision # >> nil

Try:

class Date
attr_accessor :date_precision
class << self
alias_method :old_civil, :civil
def civil(*args)
precision = args.shift
_civil = old_civil(*args)
_civil.date_precision = precision
_civil
end
end
end

date = Date.civil(“DAY_OF_MONTH”, 2004, 2, 5)
puts date.date_precision

In your original code, you were adding @date_precision to the
singleton class Date (a “class instance” variable).

-austin

austin ziegler * austin@halostatue.ca * Toronto, ON, Canada
software designer * pragmatic programmer * 2004.01.05
* 14.48.27