Syntax for union types

Lars Hansen lhansen at
Fri Nov 9 08:13:01 PST 2007

> -----Original Message-----
> From: zwetan [mailto:zwetan at] 
> Sent: 9. november 2007 07:49
> To: Lars Hansen; es4-discuss
> Subject: Re: Syntax for union types
> On Nov 9, 2007 4:31 PM, Lars Hansen <lhansen at> wrote:
> [snip]
> >
> > (More interesting open questions about the language are whether 
> > generic functions ought to be available on instances or 
> discriminating 
> > on structural types, or whether packages ought to be sealable for 
> > security, or whether ES4 precludes the use of current ES3 
> AOP patterns 
> > and how that might be solved.  Among other things.)
> >
> the option to have sealed package would be indeed an 
> interesting feature in ES4, is this is discussed somewhere in 
> the wiki ?

Not to my knowledge, and we've in any case not incorporated anything
like this.

A couple of obvious solutions would be to have package fragments
designated "final" be the only package fragment for the package, or to
have a "final"-designated package fragment provide the last fragment of
the package, preventing the loading of subsequent fragments.

Whether this is a good idea or not depends in part on whether you think
packages and namespaces are for secrecy/integrity, as implied by the use
of eg "private" in a class ("private" is just a namespace), or if
namespaces are just for collision avoidance.


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