From: "Brian Schröder" <ruby.brian@...>
Date: 2005-08-26T22:36:19+09:00
Subject: Re: symbols vs. strings

On 26/08/05, Mark Volkmann <r.mark.volkmann@gmail.com> wrote:
> On 8/26/05, Brian Schr�der <ruby.brian@gmail.com> wrote:
> > On 26/08/05, Mark Volkmann <r.mark.volkmann@gmail.com> wrote:
> > > I got the impression that when a method expects a Hash containing
> > > certain keys, I can generally specify the keys using either Symbol or
> > > String objects. So I tried this.
> > >
> > > h = {}
> > > h[:foo] = 19
> > > h['foo'] = 20
> > >
> > > and was surprised to see that those are treated as distinct entries in the Hash.
> > >
> > > So how is it that I can sometimes choose whether I want to specify a
> > > given key as either a Symbol or a String?
> > >
> > > For example, when using Tk and w represents some widget, I think I can
> > > say either
> > >
> > > w.pack(:side => 'top')
> > >
> > > or
> > >
> > > w.pack('side' => 'top')
> 
> > That can e.g. be implemented like this:
> >
> > def pack(arghash)
> >   arghash = arghash.inject({}) { | r, (k, v) | r[k.to_s] = v; r }
> >   side = arghash['side']
> >   ...
> > end
> 
> Just to clarify, are you saying that ...
> 
> 1) If I want my code that accepts a Hash parameter to allow keys to be
> either Symbols or Strings, I need to use an approach like you showed
> above.
> 
> 2) Many existing Ruby classes do this.

Yes, that is two times true. Hashes do not special-case for strings or
symbols. (Nearly) anything can go into a Hash as keys. Generally ruby
does not special case very often. Thats what makes it so nice to learn
and use.

regards,

Brian

> 
> --
> R. Mark Volkmann
> Partner, Object Computing, Inc.
> 
> 


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