Subject: Re: [xsl] Seemingly incorrect example of function subtyping in XDM 3.0 From: "Vladimir Nesterovsky" <vladimir@xxxxxxxxxxxxxxxxxxxx> Date: Wed, 26 Feb 2014 01:54:57 -0800 |
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. > > --------------------------------------- > > To invent, you need a good imagination and a pile of junk > > ------------------------------------- > > Never fight an inanimate object > > ------------------------------------- > > To avoid situations in which you might make mistakes may be the > > biggest mistake of all > > ------------------------------------ > > Quality means doing it right when no one is looking. > > ------------------------------------- > > You've achieved success in your field when you don't know whether what > > you're doing is work or play > > ------------------------------------- > > To achieve the impossible dream, try going to sleep. > > ------------------------------------- > > Facts do not cease to exist because they are ignored. > > ------------------------------------- > > Typing monkeys will write all Shakespeare's works in 200yrs.Will they > > write all patents, too? :) > > ------------------------------------- > > I finally figured out the only reason to be alive is to enjoy it.
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