Re: [xsl] Seemingly incorrect example of function subtyping in XDM 3.0

["Vladimir Nesterovsky" <vladimir@xxxxxxxxxxxxxxxxxxxx>]

I think it's better to use term covariance.
It exaclty describes the effect.

See
http://en.wikipedia.org/wiki/Covariance_and_contravariance_(computer_science)
--
Vladimir Nesterovsky
http://www.nesterovsky-bros.com

-------- Original Message --------
> From: "Michael Kay" <mike@xxxxxxxxxxxx>
> Sent: WWW W(WWW"W 26 W$WW(WWW( 2014 11:22
> To: xsl-list@xxxxxxxxxxxxxxxxxxxxxx
> Subject: Re: [xsl] Seemingly incorrect example of function subtyping in XDM
3.0
>
> I believe the example is correct.
>
> I find it useful to think of "substitutability" rather than subtyping.
>
> If the requirement is for a function that accepts a string as an argument,
then it's OK to supply a function that accepts any item as an argument. So
function(item()) is substitutable for function(xs:string).
>
> Michael Kay
> Saxonica
>
>
> On 26 Feb 2014, at 05:45, Dimitre Novatchev <dnovatchev@xxxxxxxxx> wrote:
>
> > In the W3C XDM 3.0 Proposed recommendation at the end of section:
> > "2.8.1 Functions"
(http://www.w3.org/TR/xpath-datamodel-30/#function-items)
> >
> > the last example says:
> >
> >    "function(item()) as item() is a subtype of function(xs:string) as
item()"
> >
> > I believe that the correct statement is:
> >
> >
> >    "function(xs:string) as item()     is a subtype of
> > function(item()) as item() "
> >
> > Could someone, please, confirm whether the example in the XDM 3.0 Spec
> > is correct, and if yes, then what is the chain of rules that leads to
> > this statement?
> >
> >
> > --
> > Cheers,
> > Dimitre Novatchev
> > ---------------------------------------
> > Truly great madness cannot be achieved without significant intelligence.
> > ---------------------------------------
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> > -------------------------------------
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