<?php

interface Type {}
abstract class Subtype implements Type {
  public function __construct(public readonly string $a) {}
}
class Concrete extends Subtype {}
class OtherConcrete extends Subtype {}

$result = array_map(
  static function (Concrete $i): string {
    return get_class($i) . ' - ' . $i->a;
  },
  array_filter(
    [new Concrete('a'), new OtherConcrete('b'), new Concrete('c'), new Concrete('d')],
    static function (Subtype $i): bool {
      // Comment this block out and it does not have any errors!
      if ($i->a === 'c') {
        return false;
      }
      
      return $i instanceof Concrete;
    }
  ),
);
var_dump($result);