Idea for Unit PHP extension

unit.php

<?php

$distance = new Meter(3);
$cm = $distance->in(Centimeter::class);

ecoh $distance; // 3m
echo $cm; // 300cm

$distance == Decimeter(30); // True
$distance === Decimeter(30); // False

$distance->in(Volts::class); // UnitConversionException
$distance->canConvertTo(Volts::class); // false

// Use consts, rather then methods for static analysis
class Meter extends Unit
{
    public const UNIT = "m";
    
    public const CONVERT = [
        Milimeter::class => 0.001,
        Centimeter::class => 0.01,
        Decimeter::class  => 0.1,
        Decameter::class  => 10,
        Hectometer::class => 100,
        Kilometer::class  => 1000,
    ];
}

// Disadvantage, this needs to be repeated for every distance class. Maybe use a base class
abstract class Distance extends Unit
{
    public const BASE = Meter::class;
}

class Centimeter extends Distance
{
    public const UNIT = "cm";
    public const RATIO = 0.01;
}


// Operators
$further = $distance + (new Decimeter(6));  // Meter(3.6)
$further2 = (new Decimeter(6)) + $distance; // Decimeter(36)

$closer = $distance - (new Decimeter(6)); // Meter(2.4)
$ratio = $distance / (new Decimeter(6)); // 5

// How can we do something like?
$surface = (new Meter(10)) * (new Meter(5)); // SquareMeter(50);

// Combined units ?
$m34 = new Meters(3.4);
$d34 = $d2->in(Kilometer::class, Meter::class, Millimeter::class); // Unit\Combined([Meter(3), Millimeter(400)])

echo $m34; // 3.14m
echo $d34; // 3m 400mm