Void
When you look into the 'Void', only 'null' can be seen.
Is there anybody out there?
An entry is evaluated to null
if not defined on current scope.
You can compare with null
using equality ==
or inequality !=
, like:
a == null # true, if 'a' is not defined
0 != null # true, because 0 is a defined value
Keep in mind that you can't declare an entry with no value in FatScript.
While you can assign null
to an entry, it causes different behaviors depending on whether the entry already exists in the scope and whether it's mutable or not:
- If an entry hasn't been declared yet, assigning it
null
has no effect. - If it already exists and is immutable, assigning
null
raises an error. - If it already exists and is mutable, assigning
null
removes the entry.
Delete statement
Assigning null
to a mutable entry is the same as deleting that entry from the scope. If deleted, nothing is remembered about that entry in the scope, not even it's original type.
~ m = 4 # mutable number entry
m = null # deletes m from scope
null "values" are always mutable, as in fact nothing is stored about them, and therefore they are the only kind of "value" that may transition from a mutable state to an immutable state when "reassigned"
Comparisons
You can use Void
to check against the value of an entry also, like:
() == Void # true
null == Void # true
false == Void # false
0 == Void # false
'' == Void # false
[] == Void # false
{} == Void # false
Note that Void
only accepts null
.
Another form of emptiness
Nulls can also be expressed as empty parentheses ()
and are effectively identical, in terms of behavior in code:
null == null # true
() == null # true
() == () # true