Question about instance_eval, dynamic methods and blocks

ruby-talk
1

Not sure if I am attacking this correctly or not, so if anyone has any
insight, please assist.

Let me setup my situation

class Task

  attr_reader :name

  def initialize(name, &block)
    @name = name

    instance_eval <<-EOL
      def run(&block)
        yield if block_given?
        # i need the block passed to initialize to go here
        # but i am not sure how do do it
      end
    end
  end
end

t = Task.new('do_something') { puts "I want this block to be the guts of
'run' method in t instance" }

t.run { "running #{@name}" }

basically i want to dynamically create the run method whenever i create
an instance of a task, and the guts of the run method to be the block
passed with .new but i also want the ability to have run accept a block
as well.

any help is appreciated.

···

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Posted via http://www.ruby-forum.com/.

2

Alle venerdì 14 settembre 2007, Chris Hall ha scritto:

Not sure if I am attacking this correctly or not, so if anyone has any
insight, please assist.

Let me setup my situation

class Task

  attr_reader :name

  def initialize(name, &block)
    @name = name

    instance_eval <<-EOL
      def run(&block)
        yield if block_given?
        # i need the block passed to initialize to go here
        # but i am not sure how do do it
      end
    end
  end
end

t = Task.new('do_something') { puts "I want this block to be the guts of
'run' method in t instance" }

t.run { "running #{@name}" }

basically i want to dynamically create the run method whenever i create
an instance of a task, and the guts of the run method to be the block
passed with .new but i also want the ability to have run accept a block
as well.

any help is appreciated.

I'm not sure whether I understand your question correctly. Can't you store the
block passed to initialize in an instance variable and call it from run?

class Task

  attr_reader :name

  def initialize(name, &block)
    @name = name
    @block = block
  end

  def run
    yield if block_given?
    @block.call
  end

end

If you need to create the run method dynamically for other reasons, I think
the simplest way to achieve what you want is still to store the block passed
to initialize in an instance variable:

class Task
  
  attr_reader :name

  def initialize name, &block
    @name = name
    @block = block
    instance_eval do
      def self.run
       yield if block_given?
       @block.call
      end
    end
  end

end

I hope this helps

Stefano