From: Brian Candler <B.Candler@...>
Date: 2004-10-01T17:33:22+09:00
Subject: Re: Proc.new(method)? (was Re: Funtionality of 'case'-Expression)

On Fri, Oct 01, 2004 at 09:39:55AM +0900, Markus wrote:
> > Fair enough. I'd make those criteria constants, rather than local variables
> > - perhaps in all-caps to avoid confusion with classes like Float.
> 
>      What's wrong with them being variables?  They are first class
> citizen, after all.   We can pass them around, change their value

I was just thinking of efficiency. You can declare

  NEGATIVE = Criterion.new { |x| x < 0 }

in a module or class definition, and a single persistent object is created.
However if you do this in a local variable, which by necessity is within a
method body, then every time you call that method a fresh Criterion object
will be created.

The constant also lets you share the same Criterion object between methods.

> (imagine instead of "negative" and "prime" criteria like
> "acceptable_to_most_voters" or "not_too_ugly" that may have
> (complicated) values constructed elsewhere) and in general do anything
> we want with the values.
>      So why artificially constrain their "storage class"? 

Sure, if you need a different Criterion object at different times, then
refer to it from a (local variable / instance variable / whatever)

Regards,

Brian.