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RE: F&O WD: Issue 16: Is a constructor more than a different syn tax for CAST?

From: Kay, Michael <Michael.Kay@softwareag.com>
Date: Fri, 10 May 2002 15:35:32 +0200
Message-ID: <DFF2AC9E3583D511A21F0008C7E6210602679D66@daemsg02.software-ag.de>
To: Jeni Tennison <jeni@jenitennison.com>, public-qt-comments@w3.org
Thanks. We are going to be looking at a proposal to merge constructors and
casts at our next meeting (with luck).

Michael Kay

> -----Original Message-----
> From: Jeni Tennison [mailto:jeni@jenitennison.com] 
> Sent: 09 May 2002 12:07
> To: public-qt-comments@w3.org
> Subject: F&O WD: Issue 16: Is a constructor more than a 
> different syntax for CAST?
> 
> 
> Hi,
> 
> You say that you want comments on Issue 16: Is a constructor 
> more than a different syntax for CAST?
> 
> I think that constructors are different beasts from casts 
> since a constructor implies that a literal string can be 
> tested and converted at compile time, whereas a cast implies 
> that it should be tested and converted at run time.
> 
> However, I don't think that the majority of users will 
> understand this distinction if a functional syntax is used 
> for constructors; I think that they will wonder why they can 
> do xf:date('2002-09-05') but not do xf:date(@date). There's a 
> similar situation with the
> processing-instruction() node test in XPath 1.0. Until quite 
> recently, I believed that you could do 
> processing-instruction($piName) whereas actually the 
> processing-instruction() node test has to contain a literal 
> string. I suspect that the only reason this isn't a FAQ is 
> that people don't use processing instructions much.
> 
> So I think there are two options. You could change the syntax 
> for constructors, so that the string that's interpreted to 
> construct the value doesn't look like a string, perhaps by 
> using a different delimiter, for example:
> 
>   xs:date \2002-09-05\
> 
> Or you could merge casting and construction in a functional 
> syntax, and state that if the argument is a literal string, 
> it's a static error if the string is not in the correct format.
> 
> I think that merging casting and construction is more 
> friendly to users, as it also prevents people from making the 
> "mistake" of using a cast when they could use a constructor.
> 
> Cheers,
> 
> Jeni
> ---
> Jeni Tennison
> http://www.jenitennison.com/
> 
Received on Friday, 10 May 2002 09:35:43 GMT

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