<?php
// Library code
final readonly class Renderer {
    public function __construct(private string $name, private object $object) {}
    public function render(callable $formatter): string
    {
        return $formatter($this->name, $this->object);
    }
}

// My code
$formatter = fn(string $label, object $object): string => ucfirst($label);
echo (new Renderer('name', new stdClass()))->render($formatter);