From: gwtmp01@...
Date: 2005-10-28T23:18:53+09:00
Subject: Re: Argument Passing Syntax


On Oct 28, 2005, at 5:24 AM, Sean O'Halpin wrote:

> o.[](1,2,3) { |x| p x } # this is what you have to do in 1.8
> o[1,2,3] { |x| p x }  # this causes syntax error in 1.8 but works  
> in 1.9

Here is a related thought.

Right now you can't have arguments to an "assignment method":

class A
def attribute1=(*args, &block)
   @attr1 = value
end
end

a = A.new
a.attribute1 = 4              # ok
a.attribute1(4) = 5           # syntax error
a.attribute1=(4, 5)           # syntax error
a.send(:attribute1=, 4,5)     # ok

Why not allow the middle two cases?  I think this would be helpful when
a class is wrapping one or more "containers" (Array, Hash, Set,...) and
you don't want to expose the entire interface of the container outside
of the class.  You can do this reasonably well with :[] and :[]= for a
single container but you can't have methods such as :container2[] and
:container2[]= because of the parsing problems:

     container2[index] = val    # is this self.container2.[] 
(index,val) or
                                # is this self.container2[](index,val)

But if you allowed for arguments to :container= then you could do  
something
like:

     container2(index)          # lookup contents of @container2[index]
     container2(index) = value  # modify contents of @container2[index]

Right now if you want to package multiple containers in a class you need
to create  set/get methods for each container that map to :[]/[]= for  
the
container or insert some sort of proxy class to avoid exposing the  
entire
container.

Is there a parsing hurdle to overcome or is there some conceptual reason
for prohibiting additional arguments to assignment methods?