<?php
// классы именуем в Паскаль кейсе

class SectionTree {
    static $radius = 10;
    public $hight  = 50;  // в см
    public function __construct( int $r, int $h ){
        $this->radius = $r;
        $this->hight = $h;
    }
}
class  SectionTreeChild   extends SectionTree {
    public $wight  = 50;
    public function __construct(){
         parent::__construct(233, 23);
    }
    public function getRadius() {
        return parent::$radius;
    }

}

// $obj = new SectionTreeChild();
// var_dump($obj->getRadius());


// var_dump(SectionTree::$radius);


class ChristmasTree {
    private $box = [];
    protected $color = "red";

    public function getColor(){
        return $this->color;
    }
    
    public function addSection( SectionTree $section) {
        array_push($this->box, $section);
    }

    public function debug() {
      var_dump($this->box);
    }
    public function newSection(int $r, int $h) {
       return new SectionTree($r, $h );
    }


}
// () - вызов конструктора
// $tree = new ChristmasTree();
// $s_1 = $tree->newSection(100, 20);
// $s_2 = $tree->newSection(100, 20);
// $tree->addSection($s_1);
// $tree->addSection($s_2);
// $tree->debug();


class DB {

    const SQL_SELECT_USER = 'select id, name, login 
                               from user 
                              where id = %';
    static private $_instance;
    public function __construct(){}

    static public function getInstance() {
        if (!self::$_instance) {
            self::$_instance = new self();
        }
        return self::$_instance;
    }
    const SQL_SELECT_USE = 'select id, name
                              from user 
                             where id = %';
    static public function runSQL(){
        var_dump(self::SQL_SELECT_USER);
    }
}
$obj1 = new DB();
$obj2 = DB::getInstance();
$obj3 = DB::getInstance();
DB::runSQL();
var_dump($obj1 === $obj2);