From: Robert Klemme <bob.news@...>
Date: 2005-01-19T02:16:04+09:00
Subject: Re: Creating an instance from a variable


"Bertram Scharpf" <lists@bertram-scharpf.de> schrieb im Newsbeitrag
news:20050118154256.GC7457@homer.bertram-scharpf...
> Hi Robert,
>
> Am Dienstag, 18. Jan 2005, 17:01:12 +0900 schrieb Robert Klemme:
> > "Bertram Scharpf" <lists@bertram-scharpf.de> schrieb im Newsbeitrag
> > >
> > >I'm porting my Make replacement Bake to Ruby and I do something
> > >like
> > >
> > >   class Real ; ...
> > >   class Phony ; ...
> > >
> > >   b = Builder.create target, name, prereqs, cmd
> > >
> > >where `target' is either `Real' or `Phony'.
> >
> > ???  Why can't you do
> >
> > b = target.new name, prereqs, cmd
> >
> > I mean, a class *is* a factory for its instances.  If you don't have
the
> > requirement that the actual class of created instances might be
different
> > or want to keep that flexibility I don't see any added value in
introducing
> > a method for this.
>
> Hm, seems to be a long time since I designed this. I
> remember having thought very long and thoroughly about it.

:-)

> I think I didn't tell the whole truth above. My code
> actually looks like
>
>   Rule.new   Real,  'prog', 'prog.o', 'gcc ...'
>   Rule.new   Phony, 'all',  'prog'
>   Suffix.new Real,  '.o',   '.c',     'gcc -c ...'
>
> Multiple kinds of rules can instantiate multiple types of
> targets. So, it is not possible to derive one from the
> other.
>
> Further, the suffix rule has to determine the target name
> before it holds enough information to instantiate the target
> itself.

Ok, I see.

Kind regards

    robert