XQuery quirk of the dayG. Ken Holman gkholman at CraneSoftwrights.com
Fri Apr 13 12:21:28 PDT 2012
At 2012-04-13 19:09 +0000, David Lee wrote: >Content-Language: en-US >Content-Type: multipart/alternative; > >boundary="_000_220256FDE771B74FB662165BC562CF592267FBBFCH1PRD0802MB107_" > >XQuery constantly surprises me ! >Today I was looking for a more concise way of testing if a string is >empty or blank. >The best I came up with is > > empty($s) or $s eq '' But empty($s) doesn't return true for an empty string, it returns true for an empty sequence. If $s is defined as an empty string you'll get false(): T:\ftemp>type lee.xq let $s := "" return empty($s) T:\ftemp>xquery lee.xq <?xml version="1.0" encoding="UTF-8"?>false T:\ftemp> If you know $s is a string then you can use not($s) to get true() for the empty string (and for the empty sequence) because the effective Boolean value of an empty string (and an empty sequence) is false(). >or > string-length($s) eq 0 > >But along the way discovered this > if( () eq () ) then 1 else 2 > if( () = () ) then 1 else 2 > >Returns 2 !!! > >Of course in hindsight and fine-print its correct, but entirely >non-obvious to my eye ... Just remember that the result is initialized as false() and comparisons continue until one of the two operands is the empty set or the comparison is true ... which happens right away because both operands are the empty set. I hope this helps. . . . . . . . . Ken -- Public XSLT, XSL-FO, UBL and code list classes in Europe -- May 2012 Contact us for world-wide XML consulting and instructor-led training Free 5-hour lecture: http://www.CraneSoftwrights.com/links/udemy.htm Crane Softwrights Ltd. http://www.CraneSoftwrights.com/q/ G. Ken Holman mailto:http://x-query.com/mailman/listinfo/talk Google+ profile: https://plus.google.com/116832879756988317389/about Legal business disclaimers: http://www.CraneSoftwrights.com/legal
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