From: Mike Austin <noone@...>
Date: 2006-03-08T11:33:41+09:00
Subject: Re: Having a block executed in the context of an instance

ara.t.howard@noaa.gov wrote:
> On Wed, 8 Mar 2006, Mike Austin wrote:
> 
>> I'm writing a property driven ui and would like to do things like:
>>
>> button = Button.new do
>>  caption = 'Click Me'
>> end
>>
>> I've read that 2.0 will have this feature, i.e. Class.new will execute 
>> it's block argument in it's own context.  But how do I do it in 1.8?
>>
>> Thanks much,
>> Mike
> 
>   class Button
>     def initialize(*args, &block)
>       instance_eval &block
>     end
>   end
> 
> note that you'll need to do
> 
>   self.caption = 'Click Me'

Thanks, that works well.  But as you note, prepending 'self' kind of defeats 
the purpose ;)  Is there a way to make Ruby not create local variables, but use 
  'local var' or similar?  Io (www.iolanguage.com) has this problem early on 
and was solved by using := for creating slots, and = for updating slots.  It 
would be nice if it could be lenient when running in irb, and more strict when 
executing .rb files.

> or else caption will be a local variable.  for an elegant work around 
> see the
> metakoan quiz or my traits library.  with it a really nice syntax like 
> this is
> possible

Metakoan quiz didn't turn up anything.  I looked at your traits library and it 
looks nice.  I could use an operator instead of '=' I suppose.

>   button = Button.new {
>     caption 'Click Me'
>     colour 'Orange'
>     size '42'
>   }
> 
> here's a real example from something i'm coding now:
> 
> 
>   class Flo5 < NRT::OLSSubscription::Geotiffed
>     mode "production"
> 
>     roi 47,16,39,27
> 
>     satellites %w( F15 F16 )
> 
>     extensions %w( OIS )
> 
>     solarelevations -180, -12, 10.0
> 
>     hold 0
> 
>     username "flo"
> 
>     password "xxx"
> 
>     orbital_start_direction "descending"
> 
>     start_time "2004-12-08"
>     end_time "2006-12-08"
> 
>     to_keep [ %r/.tif$/, %r/.hdr$/ ]
> 
>     tmpwatch "8 days"
>   end
> 
> 
> hth.
> 
> 
> -a

Mike