From: Brian Candler <B.Candler@...>
Date: 2007-03-01T20:55:03+09:00
Subject: Re: default passed block for method

On Thu, Mar 01, 2007 at 08:41:19PM +0900, Niko wrote:
> I'm trying to define the missing block given in the context of the 
> method to avoid the block_given? test on each iteration for yield call.
> 
>  def self.list_of_relationships(relations, source)
>    # missing_block_that_yield_would_call = lambda { || true } unless 
> block_given?
>    relations.map do |relation|
>      if yield(peer = relation.send(source))
>        [peer.display_name, peer.id]
>      end
>    end.compact
>  end

def foo(*args, &blk)
  blk ||= lambda { true }
  blk.call(*args)
end

p foo("123") { |x| "Look: #{x}" }
p foo("456")

It looks like you can't provide a default value for the block in the direct
way:

def foo(*args, &blk = lambda { true } )
  # syntax error, unexpected '=', expecting ')'
end

HTH,

Brian.