Expression helpers

in()

Checks whether a given key is present in a list or map. See Check existence of a key in a list or Check existence of a key in a map .

keys()

Accepts an attribute of type map and returns a list of key elements in the map.

len()

Computes the length of a value according to its type. Accepts an attribute of type list, map, or string and returns an integer.

• A listreturns the number of elements in the list.
• A mapreturns the number of key-value entries stored in the map.
• A stringreturns the number of characters in the string.

default(val, defaultVal)

Returns a value if it is not null; otherwise returns a default value.

• If not null , val is returned.
• If val is null , defaultVal is returned.

You can use default with the standard library function, map.get , to safely access optional values in a map, returning null if the key is not found. For an example, see Read map values .

You can also use default to access optional runtime arguments, and return a default value if the key is not found. For an example, see Access runtime arguments .

if(condition, ifTrue, ifFalse)

Evaluates a condition and returns one of two arguments depending on what the condition evaluates to.

• If condition evaluates to true, ifTrue is returned.
• If condition evaluates to false or null , ifFalse is returned.

Note that arguments passed to if are always evaluated and that the function does not control processing flow. To conditionally execute an expression, use a switch statement. For more information, see Conditions .