The ZPE is_set feature has been included as a YASS language keyword since ZPE 1.12.4. Prior to
this it was a predefined function which can be found here.
is_set determines if a variable has already been defined locally, globally or as a parameter. This is particularly useful for determining if
an optional parameter has been defined. This will provide a boolean value.
Using is_set
The is_set feature works like a function syntactically but it differs in it's
implementation.
$a = 10 print(is_set($a)) $b = {a : 15} print(is_set($b->a))
Unlike prior versions, is_set cannot be used on pure values
and must be used on expressive values.
Before becoming a keyword
Prior to is_set becoming a language keyword, the
is_set was a function. Part of the design philosophy
behind making a keyword was to make execution faster as it was a widely used
function but whilst maintaining compatibility with existing scripts.
The is_set function is one of the oldest functions
in ZPE. You can read more about it here.
