Primary Constructors

Hello internals,

I was reminded of my records RFC today, and one of the features of the RFC was "short constructors" generally called "primary constructors" in C#/Kotlin.

They would look like this:

class Point(public int $x, int $id = 0) extends Base($id);

Which is just sugar for this:

class Point extends Base {
public function __construct(public int $x, int $id = 0) {
parent::__construct($id);
}
}

or this:

class Point extends Base {
public int $x;
public function __construct(int $x, int $id = 0) {
$this->x = $x;
parent::__construct($id);
}
}

A class with a primary constructor may not have a defined __construct function. Any special initialization must be done with hooks:

class Temperature(
public float $celsius {
set {
if ($value < -273.15) {
throw new ValueError('below absolute zero');
}
$this->celsius = $value;
}
}
) {}

new Temperature(20.0); // ok
new Temperature(-300.0); // ValueError: below absolute zero

I'm sending this email to the list to gather additional feedback before pursuing a formal RFC proposal.

— Rob

I just realized that my examples did not demonstrate the classes with a body, but they may also have a body!

— Rob