Maps—also called hashes, dictionaries, and associative arrays—are created by enclosing comma-delimited name-value pairs in curly braces, like so:

some_hash = {"foo" : "bar", 
"fizz" : {"a" : 5, "b" : 6}, 
"flop" : [1, 2, 3]};

Maps can be queried in the traditional manner using a key enclosed in curly braces:

my_val = some_hash{"foo"}; // returns "bar"

KRL allows deep queries by what are known as hash paths. A hash path is an array whose elements represent the key values (for a map) or array indices of a path from the root of a complex data structure to the element of interest:

another_val = some_hash{["fizz", "b"]}; // returns 6

There are a number of map operators that affect maps.

For example, to retrieve all values from the map, you use the values() operator:

my_vals = some_hash.values(); // returns ["bar", {"a" : 5, "b" : 6}, [1, 2, 3]]

As another example, you can also merge hashes using the put() operator:

new_map = {"foo" : "bar1", "bazz": 4};
// returns {"foo" : "bar1", "fizz" : {"a" : 5, "b" : 6}, "flop" : [1, 2, 3], "bazz": 4}

When defining map literals, a string literal must be used to define the keys. This code will not work.

some_string = "map_key";
literal_map = {some_string : "associated value"}; // DOES NOT WORK

You must use the put() operator to add string values bound to variables as keys for a map. 

For example:

first_key = "map_key";
second_key = "second_map_key";
new_map = {}.put(first_key, "first entry").put(second_key, "second entry");

new_map looks like this:

  "map_key": "first entry",
  "second_map_key": "second entry"

Operations on Maps

There are a number of operators that work on maps. In addition there is an map membership infix operator.

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