Hello!
Thank you very much, I will read. What I skimmed now, there exists *subtype substitution*, which would allow xs:positiveIntegers be automaticall cast to xs:integers, which is the opposite direction of my case. There exists also *type propagation*, which of one case allows any xs:decimal or subtype of it be cast into either xs:double or xs:float, which can result in a loss of precision.
I guess my intuition put together, that if it's possible to substitute with subtypes && it's possible to propagate from decimals to floats and doubles, then it ought to be possible to move also along the non-destructive parts of sub and supertypes. Nothing is ideal, atleast I can explicitly cast the return value as xs:positiveInteger.
PS for my further investigations, could you point me to the BaseX code for the pseudo-function named derives-from? Thank you!
Best regards Kristian
15.04.2015 16:19, Christian Grün kirjutas:
Hi Kristian,
Why can't I specify xs:positiveIntegers as literals? Or why can't I treat xs:integers as xs:positiveIntegers?
The error is correct. Type handling in XQuery is a topic on its own: Values can be cast, promoted, treated as, etc. in this language. If you want to dive into the details, I suggest having a look at the section on type promotion in the specification:
http://www.w3.org/TR/xquery-31/#id-type-promotion-and-operator-mapping
If you are looking for a practical solution, I advise you to simply use with xs:integer, even if a value will always be positive, or if it will have a smaller bit range. Most operations have been optimized for integers, so you won't lose any time for additional type conversion.
Hope this helps, Christian
Consider a simple function that takes a
xs:positiveInteger as input:
<code> xquery version "3.0" encoding "UTF-8"; declare namespace local = "local";
declare function local:positive( $input as xs:positiveInteger ) as xs:positiveInteger { $input };
</code>
I get an error XPTY0004 Cannot treat xs:integer as xs:positiveInteger if I run it with a literal input, like this:
<code> local:positive(2) </code>
I get no error if I specify the type explicitly, like this:
<code> local:positive(xs:positiveInteger(2)) </code>
This feel very odd, since the type system is hierarchical and xs:positiveInteger is a subcase of xs:integer, I don't really see a problem of this kind of automatic casting of integer literals if they qualify the cast.
Can you give any reflection on this?
Best regards Kristian Kankainen