From: ts <decoux@...>
Date: 2001-04-18T01:49:56+09:00
Subject: [ruby-talk:13768] Re: Odd Hash Behavior (long)

>>>>> "S" == Steve Tuckner <SAT@MULTITECH.com> writes:

S> I am kind of new to Ruby, could you explain the change to the hash class in
S> detail (it might be good for other newbies too)?

 I'll try but personnally I'm not good in english :-)

S> pigeon% cat b.rb
S> #!/usr/bin/ruby
S> class << Hash 

S>    alias :old_new :new

 it create an alias old_new on the method new (i.e. it save the old
definition of new in old_new)

S>    def new(default = nil, &block)

 it redefine the method Hash::new which can take an optional argument and
can be called with a block (as an iterator)

S>       a = old_new(default)

 it call the old definition of new

S>       if block_given?

 if Hash::new was called with a block

S>          raise "Invalid call" if default
S>          a.instance_eval <<-EOT

 it will redefine the method [] only for this object

S>             @block = block

 it save the block given to #new in an instance variable (specific to this
 object) 

S>             alias :aref :[]
S>             def [](a)

 redefinition of []

S>                if ! has_key?a 

 if the key don't exist, it call the block and store the result in the hash

S>                   self[a] = @block[]
S>                end
S>                aref(a)

 it retrieve the value (call the old method [])

S>             end
S>          EOT


Guy Decoux