Generics: Type Erasure #

Type Parameters are erased at runtime. This means that the type parameters are not available at runtime.

Example #

function foo(vec<int> $integers): void {
    var_dump($integers);
}

function bar(): void {
    foo(vec["foo", "bar"]);
}

The compiler will emit a type error for the call to foo() in bar() because the type of the argument is vec<string>, which is not a subtype of vec<int>.

If we ignore the error using --ignore flag, the code will compile and run, however, ignoring type errors is highly discouraged, as it can lead to runtime errors.

Limitations #

Due to the type erasure, the following features are not supported:

• Type parameters in instanceof expressions ( if ($value instanceof Foo<T>) { ... } )
• Type parameters in is expressions ( if ($value is Foo<T>) { ... } )
• Type parameters in as expressions ( $value as Foo<T> )
• Type parameters in new expressions ( new T() )
• Type parameters in catch blocks ( try { ... } catch (T $e) { ... } )

For passing around class names, Ara has classname<T> type, which can be used to create instances of a specific class.

Example:

interface Foo<T> {
    public function __construct(T $value);
}

function foo<T>(classname<Foo<T>> $class, T $value): void {
    $instance = new $class($value);

    var_dump($instance);
}