From: "David A. Black" <dblack@...>
Date: 2004-11-15T06:07:10+09:00
Subject: Re: I guess "obj.attr = arg" methods don't allow blocks... (maybe rcr?)

Hi --

On Mon, 15 Nov 2004, Sam Roberts wrote:

> 
> Does this conflict with some kind of basic rule in the grammer?

Well... I suspect it conflicts with a basic intention, which is to
make these = methods callable in a way that looks and acts as close to
assignment as possible. 

> Could it be an RCR, or is just wrong-headed? :-)
> 
> I want to assign into an object, but I want to take a proc as an arg, so
> that the assignment can be "paramaterized" in some sense, like;
> 
> # Usually:
> card.email = "user@example.com"
> 
> # Sometimes:
> card.email = "user@example.com" do |e|
>   e.type = 'preferred'
>   e.protocol = 'uucp'
>   e.location = 'work'
> end
> 
> It doesn't seem to be allowed, I did a quick test:

It's such a hybrid: it's a method call trying to look like an
assignment trying to act like a method call.  It thus ceases to be
assignment emulation, so I don't think it would make sense.  

> I also tried to do a = method with two args, the second optional.
> 
> It prints nothing, but runs, which makes me wonder what its doing!

It's like:

  a = 1,2             # a == [1,2]

  a.x = 1, Proc.new   # a.x= is called with arg of
                      #      [1, #<Proc:0000....>]

Again, the idea is to emulate assignment.  In fact, look at this:

irb(main):007:0> class C; def x=(y); @x = y; end; def x; @x; end; end
# Yes I do know I've inlined an attr_accessor  call :-)
=> nil
irb(main):008:0> c = C.new
=> #<C:0x401c7434>
irb(main):009:0> c.x,d = 1,2     #### This line in particular
=> [1, 2]
irb(main):010:0> c.x
=> 1
irb(main):011:0> d
=> 2


David

-- 
David A. Black
dblack@wobblini.net