From: Robert Klemme <bob.news@...>
Date: 2005-02-01T17:10:50+09:00
Subject: Re: Default values for block parameters


"Matt Mower" <matt.mower@gmail.com> schrieb im Newsbeitrag
news:d563731905013110444211811e@mail.gmail.com...
> Hi Robert,
>
> On Tue, 1 Feb 2005 03:30:46 +0900, Robert Klemme <bob.news@gmx.net>
wrote:
> >
> > "Matt Mower" <matt.mower@gmail.com > schrieb im Newsbeitrag
> > news:d563731905013109382bbeef75@mail.gmail.com...
> > > Hi.
> > >
> > > I want to dynamically create (i'm trying to use define_method) a
> > > method using which has default values for it's parameters.  However
> > > when I try to do:
> > >
> > >     define_method "name" lambda { |x=1,y=2,z=3| f(x,y,z) }
> > >
> > > I get a syntax error on the x=1 part.   Am I just using the wrong
> > > syntax?  Or is it really not possible to create methods with default
> > > parameter values dynamically?
> >
> > I guess you will have to do
> >
> > define_method( "name" ) { |*a| f(a[0]||1, a[1]||2, a[2]||3) }
> >
> > Or something similar.
> >
>
> Ah, thank you -- I had thought of using || to get the defaults but not
> to use |*a| to allow parameters to be passed, or not, which is the
> vital bit.
>
> Since this workaround is a touch unaesthetic I wonder whether there
> was a particular reason for not allowing default values to be
> specified for block parameters?  Do you happen to know?

Dunno, but here's my guess: since blocks are usually called at a single
place in code (as opposed to a method) default parameters do not make much
sense generally.

Kind regards

    robert