From: nvp <ruby-lists@...>
Date: 2008-10-29T02:21:41+09:00
Subject: lambda and multiple arguments: how?!

Hello,

I've been working on porting a useful Perl module to Ruby and have
been struggling with the differences between Perl's function
references and Ruby's lambda, proc, etc.

Basically, my Perl module has two functions that do this:

  sub run_on_finish { my ($s,$code,$pid)=@_;
    $s->{on_finish}->{$pid || 0}=$code;
  }

  sub on_finish { my ($s,$pid,@par)=@_;
    my $code=$s->{on_finish}->{$pid} || $s->{on_finish}->{0} or return 0;
    $code->($pid,@par);
  };

Using the above, I can do the following:

  $obj->run_on_finish(sub { my($pid, $exit_code, $ident) = @_;
  # Do something with $pid, $exit_code, $ident
  });

In Ruby, things are more difficult given that I don't fully understand
closures yet.  I've reimplemented the methods like so:

  # module
  def run_on_finish(code, pid=0)
    begin
      self.do_on_finish[pid] = code
    rescue
      raise "error in run_on_finish\n" # Message stinks
    end
  end

  def on_finish(pid, *params)
    code = self.do_on_finish[pid] || self.do_on_finish[0] or return 0
    begin
      code.call(pid, params)
    rescue
      raise "lameness\n" # Message stinks
    end
  end

  # client
  pfm.run_on_finish(
    lambda {
      |pid,exit_code,ident|
      print "LEN ", pid.length(), " -- ", "MY ARGS ", pid.join(':'), "\n"
    }
  )

As you can see, I'm calling self.do_on_finish with the arguments
'pid', and an array of 'params'.
Unfortunately Ruby only matches |pid,<second_arg>|, and this is not
the behavior I'd expect or
want.

Outside of setting |*params| in lambda {} such that I would check/set
my values manually, is
there a way to provide lambda with more than two arguments?

-- 
nvp
"Of course, the US has many elements of socialism already since
capitalists, like cats, tend to get themselves stuck up a tree every
so often."  -- Joe Johnston