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1798 Function fn:function-identity #1801

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Mar 5, 2025
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1798 Function fn:function-identity #1801

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dnovatchev Feb 15, 2025
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dnovatchev Feb 15, 2025
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fn:function-identity
dnovatchev Feb 15, 2025
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Reflected MHK's comment
dnovatchev Feb 16, 2025
f2daf25
Merge branch 'master' of https://github.com/dnovatchev/qtspecs into d…
dnovatchev Feb 19, 2025
5cbb1ae
Removed the DM note that maps and arrays don't have identity. As per …
dnovatchev Feb 19, 2025
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dnovatchev Feb 25, 2025
9b8f8f2
Maps/arrays also have identity now
dnovatchev Feb 25, 2025
3ec6eba
Merge branch 'master' of https://github.com/dnovatchev/qtspecs into d…
dnovatchev Mar 5, 2025
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4 changes: 0 additions & 4 deletions specifications/xpath-datamodel-40/src/xpath-datamodel.xml
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Expand Up @@ -5547,10 +5547,6 @@ identity, equality, or otherwise, and</phrase> have no serialization.
when functions appear in the arguments supplied to the <code>fn:deep-equal</code> function;
and secondly, in establishing whether the arguments and results of a function are "the same"
when deciding whether the function is deterministic.</p></note>

<note><p>Function identity is not currently defined for maps and arrays, because in the circumstances
where function identity would otherwise be used, maps and arrays are compared by examining their
content.</p></note>
</item>
<item>
<p>
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34 changes: 34 additions & 0 deletions specifications/xpath-functions-40/src/function-catalog.xml
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Expand Up @@ -20768,6 +20768,40 @@ return function-arity($initial)</eg></fos:expression>
</fos:example>
</fos:examples>
</fos:function>
<fos:function name="function-identity" prefix="fn">
<fos:signatures>
<fos:proto name="function-identity" return-type="xs:string">
<fos:arg name="function" type="fn(*)"/>
</fos:proto>
</fos:signatures>
<fos:properties>
<fos:property>deterministic</fos:property>
<fos:property>context-independent</fos:property>
<fos:property>focus-independent</fos:property>
</fos:properties>
<fos:summary>
<p>Returns the identity of the function item.</p>
</fos:summary>
<fos:rules>
<p>The <function>fn:function-identity</function> function returns the identity of
the function identified by <code>$function</code>.</p>
</fos:rules>
<fos:notes>
<p>This function can be useful in any scenario, where the evaluation of a function call
requires repeated evaluation of this same, or other functions. Often in such cases,
the algorithm needs access to a general structure, containing the cached results of executing
possibly many different functions applied on specific arguments-tuples.
A unique key is needed under which to group all invocations of a specific function
and then the mapping between their function-call arguments and the result of the call.
The identity of a function fits exactly the requirements (uniqueness / one per function) for such a key.</p>
<p>The function identity, by definition, is generated upon the creation of a function, is implementation-defined,
and has meaning throughout the life of that function. It is not meaningful to store this value
across different executions, because the identity given to a function in <code>execution1</code> will generally be different
from the identity, given to it in <code>execution2</code>.</p>
<p>The function identity, being a string, can be used as a key in a map, thus making it possible
to map a particular function to a sequence of items.</p>
</fos:notes>
</fos:function>

<fos:function name="function-annotations" prefix="fn">
<fos:signatures>
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3 changes: 3 additions & 0 deletions specifications/xpath-functions-40/src/xpath-functions.xml
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Expand Up @@ -7503,6 +7503,9 @@ return <table>
<div3 id="func-function-arity">
<head><?function fn:function-arity?></head>
</div3>
<div3 id="func-function-identity">
<head><?function fn:function-identity?></head>
</div3>
<div3 id="func-function-annotations">
<head><?function fn:function-annotations?></head>
</div3>
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