On Tue, 1 Feb 2005 17:10:50 +0900, Robert Klemme <bob.news / gmx.net> wrote:
> 
> "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.

I think that's a good assessment... I think historically, they may
have been considered superfluous. But it could change in the future;
with the addition of &block syntax in a block's parameter list
(available now, in 1.9, and later, in 2.0), it might be that block
parameter lists are going to be made more consistent with method
parameter lists.

Maybe :)

cheers,
Mark

> 
> Kind regards
> 
>     robert
> 
>