map:get

map:get(
    $map as map(*), 
    $key as xs:anyAtomicType
) as item()*

This function is deterministic, context-independent, and focus-independent.

The function map:get attempts to find an entry within the map supplied as $map that has the same key as the supplied value of $key. If there is such an entry, it returns the associated value; otherwise it returns an empty sequence.

A return value of () from map:get could indicate that the key is present in the map with an associated value of (), or it could indicate that the key is not present in the map. The two cases can be distinguished by calling map:contains.

Invoking the map as a function item has the same effect as calling get: that is, when $map is a map, the expression $map($K) is equivalent to map:get($map, $K). Similarly, the expression map:get(map:get(map:get($map, 'employee'), 'name'), 'first') can be written as $map('employee')('name')('first').

let $week := map{0:"Sonntag", 1:"Montag", 2:"Dienstag",
     3:"Mittwoch", 4:"Donnerstag", 5:"Freitag", 6:"Samstag"}

The expression map:get($week, 4) returns "Donnerstag".

The expression map:get($week, 9) returns (). (When the key is not present, the function returns an empty sequence.)

The expression map:get(map:entry(7,()), 7) returns (). (An empty sequence as the result can also signify that the key is present and the associated value is an empty sequence.)