Re: Simple map and string-length(): unexpected behavio

Convoluted history here. The XPath 1.0 spec is:

<quote>
Function:B numberB string-length(string?) <>
The string-length
<https://www.w3.org/TR/1999/REC-xpath-19991116/#function-string-length>
returns the number of characters in the string (see [3.6 Strings]
<https://www.w3.org/TR/1999/REC-xpath-19991116/#strings>). If the argument is
omitted, it defaults to the context node converted to a string, in other words
the string-value
<https://www.w3.org/TR/1999/REC-xpath-19991116/#dt-string-value> of the
context node.

</quote>

(Yes, that's the entire spec). In 1.0, if you supplied something other than a
string, it would be implicitly converted to a string by calling the string()
function, by virtue of the rules for function calls. Recall also that 1.0 only
had a context node, not a context item (without something like the "!"
operator, there was no way the context item could be a number.)

In 2.0 the spec became:

<quote>
7.4.4 fn:string-length

fn:string-length() as xs:integer
fn:string-length($arg as xs:string?) as xs:integer
Summary: Returns an xs:integer equal to the length in characters of the value
of $arg.

If the value of $arg is the empty sequence, the xs:integer 0 is returned.

If no argument is supplied, $arg defaults to the string value (calculated
using fn:string() <https://www.w3.org/TR/xquery-operators/#func-string>) of
the context item (.). If no argument is supplied and the context item is
undefined an error is raised: [err:XPDY0002
<http://www.w3.org/TR/xpath20/#ERRXPDY0002>]XP.

</quote>

Spot the difference.

I don't know if it was recognized at the time, but the way that is written
means that string-length() and string-length(.) do different things. If the
context item is a number, string-length() converts the number to a string,
whereas string-length(.) gives you a type error unless XPath 1.0 compatibility
mode is in force.

If (like other functions that take the context item as an implicit argument)
the spec had simply said that the first argument defaults to "." (the context
item), it would still have been backwards compatible with 1.0 in all cases
when backwards compatibility was enabled, without introducing this anomaly.

Michael Kay
Saxonica


> On 8 Jun 2019, at 01:52, Elisa Beshero-Bondar ebbondar@xxxxxxxxx
<xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> Dear XSL list,
>
> We are perplexed by a discrepancy between applying the string-length()
function directly to a numerical argument and using simple map to perform what
we expected would be the same operation. string-length(5) returns an error, as
expected. oXygen reports: "XPath failed due to: Required item type of first
argument of fn:string-length() is xs:string; supplied expression (5) has item
type xs:integer". eXist-db reports: "xs-integer(5) is not a sub-type of
xs-string".
>
> When we use simple map, though, the behavior is different:
>
> 5 ! string-length() returns a string-length of 1
>
> 05 ! string-length() returns a string-length of 2
>
> 0.5 ! string-length() returns a string-length of 3
>
> 00.5 ! string-length returns a string-length of 3
>
> 05 ! string-length() returns a string-length of 1
>
> Can someone please explain why simple-map does not raise the type error that
we see when we write the numerical argument directly inside the function
parentheses?
>
> Thanks for your help!
> Elisa
> --
> Elisa Beshero-Bondar, PhD
> Associate Professor of English
> University of Pittsburgh at Greensburg
> Humanities Division
> 150 Finoli Drive
> Greensburg, PA  15601  USA
> E-mail: ebb8@xxxxxxxx <mailto:ebb8@xxxxxxxx>
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