From: Wes Bailey <wes@...>
Date: 2010-05-31T07:17:42+09:00
Subject: Re: Inject Loop Syntax


----- "Intransition" <transfire@gmail.com> wrote:

> On May 30, 5:35 am, Robert Klemme <shortcut...@googlemail.com> wrote:
> > On 29.05.2010 21:47, Intransition wrote:
> >
> >
> >
> > > I wonder if any other languages have any sort of "multiplicative
> > > operation" operator. I was thinking about this today b/c sometimes
> one
> > > has to use a block where it would read better if it could be
> avoided.
> > > For example:
> >
> > >    [:a, :b, :c].each do |x|
> > >      define_method("#{x}?") do
> > >        instance_variable_get("@#{x}")
> > >      end
> > >    end
> >
> > > I completely made this up off the top of my head, so ignore what
> it
> > > actually does. The point is rather it would be cool if the loop
> could
> > > described without encasing the code, something like:
> >
> > >    define_method("#{x}?") do<-(x)[:a, :b, :c]
> >
> > This can never work because the string is evaluated before the
> method
> > call so you would be defining the same method over and over again
> (if x
> > is actually defined in the surrounding scope).
> >
> > >      instance_variable_get("@#{x}")
> > >    end
> >
> > > It is kind of like HERE documents, but applied to code. Of course
> I am
> > > not sure about the syntax either.
> >
> > I don't see a solution that is better than the explicit loop you
> > presented initially.
> 
> Yea, I didn't really expect it could be done in Ruby as it now
> stands.
> Though there is this bit of craziness:
> 
>   class X
>                               lambda { |x|
>     define_method("#{x}") do
>       instance_variable_get("@#{x}")
>     end                       }.call_for_each(:a, :b, :c)
> 
>   end
> 
> :-)

irb(main):074:0> class MyTest
irb(main):075:1> class_eval %w/a b c/.inject( '' ) { |methods,var| methods + "def hello_#{var}?; puts \"hello_#{var}\"; end\n" }
irb(main):076:1> end
=> nil
irb(main):077:0> t = MyTest.new
=> #<MyTest:0x86e98>
irb(main):078:0> t.hello_a?
hello_a
=> nil
irb(main):079:0> t.hello_b?
hello_b
=> nil
irb(main):080:0> t.hello_c?
hello_c
=> nil