Argument-Less Functions
Following is a constant:
and this is a function:
The definition below is like neither a constant nor a function:
This is a function with no arguments, but it is not a constant. Like a constant, you can call this definition without an argument list, that is, you can call Age using an expression like Age instead of Age(). Also like a constant, this definition stores its value in the calculated value property. However, unlike a constant, this definition does not set its evaluation flag. Every time you call the definition, it executes again.
Definitions like this are useful when you have a node you want to evaluate more than once but you do not want to evaluate it every time you use its value. When you want the node to execute, just call it normally (e.g., Age). When you just want to recall the node's value from the last evaluation, use the Value Of operator (e.g., ?Age).
See Value Of.