Classes: Properties
A property is a variable defined in a class.
class Counter
{
public int $value = 0;
}
INFO
Every instance has a separate value for an instance property.
Property Access
Refer to Expressions: Object Operations - Property Access for more information.
Initializing Properties
Properties in Ara must be initialized, either using a default value, or in the constructor.
class DefaultValues {
public int $value = 0;
}
class SetInConstructor {
public int $value;
public function __construct() {
$this->value = 0;
}
}
Property Visibility
A property can be declared as public, protected, or private.
class Counter {
public int $value = 0;
protected int $value = 0;
private int $value = 0;
}
Read-only Properties
A property can be declared as readonly.
class Counter {
public readonly int $value = 0;
}
WARNING
Unlike other properties, a read-only property cannot be initialized with a default value.
class Counter {
public readonly int $value = 0;
}
The code above will result in the following error:
error[P0018]: readonly property `Counter::$value` cannot have a default value
┌─ examples/readonly-with-value.ara:3:23
│
1 │ class Counter {
│ -------
2 │ public readonly int $value = 0;
│ -------- ^^^^^^^^^^ readonly property `Counter::$value` cannot have a default value
│
= note: a readonly property cannot have a default value because it cannot be changed after initialization.
= help: try removing the default value.
Static properties
A static property is a property that is shared between all instances of a class.
class Counter {
public static int $value = 0;
}
To access a static property, use :: operator.
function main(): void {
Counter::$value = 1;
}
INFO
If your property never changes value, you might want to use a class constant instead.
WARNING
A static property cannot be declared as readonly.
class Counter {
public static readonly int $value;
}
The code above will result in the following error:
error[P0017]: readonly property `Counter::$value` cannot be static
┌─ examples/static-readonly-property.ara:2:12
│
1 │ class Counter {
│ -------
2 │ public static readonly int $value;
│ ^^^^^^ -------- ------
│ │
│ readonly property `Counter::$value` cannot be static
│
= note: a property cannot be both readonly and static.
= help: try removing `static`.
Static Property Access
Refer to Expressions: Class Operations - Static Property Access for more information.
The Property Namespace
Properties and methods are in different namespaces. It's possible to have a method and a property with the same name.
class Counter {
public int $value = 0;
public function value(): int
{
return $this->value;
}
}
WARNING
Using the same name for a method and a property can be confusing. We recommend you using different names.
$b->value(); // method call
$b->value; // property access
If you want to call the value of a property that has Closure type, you will need to be explicit that you're accessing the property.
class IntAdder {
public Closure<(int, int), int> $callable;
public function __construct() {
$this->callable = function(int $a, int $b): int {
return $a + $b;
};
}
}
You can do this by using parentheses.
function main(): void {
$adder = new IntAdder();
($adder->callable)(1, 2); // 3
}