Nullability
In abstract, for security reasons, all data and data reference is assumed to exist and be acessable as default . However, very often is usefull to have a way to identify if a data, object or reference exists and is acessible or not.
Abstract allows to specify when a data can be expected to be nullable or not, also allowing a variety of security features to prevent errors when acessing null values.
The nullable wrapper
Abstract allows to declarate nullable types wrapping them with the nullable structure.
This wrapping can be also easily made putting the interrogation (?) character right
before the desired type.
?void # same as Std.Types.Nullable(void)
?i32 # same as Std.Types.Nullable(i32)
?string # same as Std.Types.Nullable(i32)
Managing wrapped values
The language also provides some features to make the life using nullable types esier.
Getting the data
The nullable wrapper will not allow you to access the data directly.
func ?i32 foo() { ... }
# This is a compilation error!
let i32 myNumber = foo()
Instead, you have two options to acess the internal data:
Checking if the value is not null or ignoring the possibility of a null value.
you can easily check the existence of the value using a conditional statement and use the unrapped value in the condition scope as follows:
func ?i32 foo() { ... }
let ?i32 myNumber = foo()
if (myNumber) {
# Inside the if scope, `myNumber` is shadowed
# to unwrap the value
let i32 value = myNumber
}
# Compilation Error! `?i32` is not assignable to `i32`
let i32 value = myNumber
Or ignore the check and manually unrap the condition using the .unwrap() call
or the ? operator:
func ?i32 foo() { ... }
let i32 myNumber = foo()?
### is the same as ###
let i32 myNumber = foo().unwrap()
If you have a default value to use in case of null, you can use the ?? operator to
try to unwrap the expression and use the next expression if it's null:
func ?i32 foo() { ... }
let i32 value = foo() ?? 0
### is the same as ###
let i32 value
let ?i32 nullable = foo()
if (nullable) value = nullable
else value = 0