Copying parameters to singleton class

Ruby
21

7stud – wrote in post #992632:

Try something like this:

def using(new_options)
Class.new(self) do
old_options = superclass.options
common_keys = old_options.keys & new_options.keys

    common_keys.each do |key|
      old_options[key] = new_options[key]
    end

    @options = old_options
    @options.freeze
  end
end

Whoops. That doesn’t work:

prog.rb:18:in `[]=’: can’t modify frozen hash (RuntimeError)

Hmmm…why can you merge() but not directly assign to individual keys
when a hash is frozen?

Ok, merge() with some better variable names:

def using(new_options)
Class.new(self) do
old_options = superclass.options

    @options = old_options.merge(new_options).select do |key|
       old_options.has_key?(key)
    end.freeze
  end
end
22

Lars O. wrote in post #992715:

On 14 Apr, 03:09, 7stud – [email protected] wrote:

 old_options[key] = new_options[key]

 old_options.has_key?(key)
end.freeze

end
end

–
Posted viahttp://www.ruby-forum.com/.

Hi!

Even though I agress that using the same name for both the local
parameter and a method with the same name might be a bad idea, my code
still works without any problem. If I redefine self using to:

There’s working code, and there’s clear code. The goal is working code
that is clear!

Hmmm…why can you merge() but not directly assign to
individual keys when a hash is frozen?

Duh. Because merge() produces a new hash–it doesn’t change the frozen
hash.

23

On 14 Apr, 03:09, 7stud – [email protected] wrote:

 old_options[key] = new_options[key]

 old_options.has_key?(key)
end.freeze

end
end

–
Posted viahttp://www.ruby-forum.com/.

Hi!

Even though I agress that using the same name for both the local
parameter and a method with the same name might be a bad idea, my code
still works without any problem. If I redefine self using to:

(minor change to last version. I split up the calls to merge, select,
and freeze to its own rows.)

def self.using(options)
Class.new(self) do
puts “Superclass options: #{superclass.options.inspect}”
puts “Options from parameter: #{options}”
@options = superclass.options.merge(options)
@options.select! { |key, value| superclass.options.has_key?
(key) }
@options.freeze
end
end

it clearly shows that options (by itself) refers to the local paramter
and not the class name.

/lasso