Block that takes a block

ruby-talk
1

How can I make a block that takes a block argument? This doesn't parse:

myproc = proc{|&blk| [1,2,3].each(&blk)}

The main reason I want to do this is to create a method with
'define_method' that takes a block argument.

For example, the 'before' method below works fine, until you apply it
to a method that takes a block.

class Object
  # Is there a built-in way to do this?
  def metaclass; class << self; self; end; end

  # Call blk before each invocation of method_name
  def before(method_name, &blk)
    oldblk = method(method_name)
    metaclass.instance_eval {
      define_method(method_name){|*args|
        blk.call(*args)
        oldblk.call(*args)
      }
    }
  end
end

thanks,
Ed

2

I believe this is a limitation in the current 1.8 series. This has
been lifted in HEAD.

You might want to consider using a smart intermediate method that is a
wrapper around the block which can safely take an instance of Proc.

Brian.

···

On 9/20/05, Edward Faulkner <ef@alum.mit.edu> wrote:

How can I make a block that takes a block argument? This doesn't parse:

myproc = proc{|&blk| [1,2,3].each(&blk)}

The main reason I want to do this is to create a method with
'define_method' that takes a block argument.

For example, the 'before' method below works fine, until you apply it
to a method that takes a block.

class Object
  # Is there a built-in way to do this?
  def metaclass; class << self; self; end; end

  # Call blk before each invocation of method_name
  def before(method_name, &blk)
    oldblk = method(method_name)
    metaclass.instance_eval {
      define_method(method_name){|*args|
        blk.call(*args)
        oldblk.call(*args)
      }
    }
  end
end

thanks,
Ed

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