Provides mechanism for read-only property that relieves __get implementation.

ProperyReadable.php

<?php
/**
 * PropertyReadable.php
 *
 * (c) 2018 koohq. Licensed under CC0.
 * https://creativecommons.org/publicdomain/zero/1.0/legalcode
 */
trait PropertyReadable
{
    /** @var array [string => string|callable] */
    protected $accessors = [];
    
    public function __get($name)
    {
        if (isset($this->accessors[$name])) {
            $accessor = $this->accessors[$name];

            if (is_string($accessor) && property_exists($this, $accessor)) {
                return $this->$accessor;
            }

            if (is_callable($accessor)) {
                return call_user_func($accessor);
            }
        }
    }
}

Sample.php

<?php
/**
 * @property-read string $name
 * @property-read string $altName
 * @property-read bool $isNameEmpty
 * @property-read bool $isNameNull
 * @property-read int $count
 * @property-read int $randomInt
 */
class Sample
{
    use PropertyReadable;
   
    /** @var string $name */
    private $name;
    
    /** @var int $time Unix timestamp when $this is created */
    private $time;
    
    public function __construct($name)
    {
        $this->name = (string)$name;
        $this->time = time();
 
        // Register accessors
        $this->accessors = [
            // propertyName => propertyName [this returns $this->name]
            'name' => 'name',
            // propertyName => otherPropertyName [Alias]
            'altName' => 'name',
            // propertyName => propertyName(also globalFunction) [this returns $this->time, not time()]
            'time' => 'time',
            // propertyName => closure
            'isNameEmpty' => function () { return empty($this->name); },
            // propertyName => instanceMethod
            'isNameNull' => [$this, 'isNameNull'],
            // propertyName => staticMethod
            'count' => 'self::countUp',
            // propertyName => globalFunction [this returns rand()]
            'randomInt' => 'rand',
        ];
    }

    /** @return bool indicates $this->name is null */
    private function isNameNull()
    {
        return $this->name === null;
    }

    /** @return int number that is incremented on each call */
    private static function countUp()
    {
        static $counter = 0;
        return $counter++;
    }
}

/**
 * Sample (No use PropertyReadable)
 *
 * @property-read string $name
 * @property-read string $altName
 * @property-read bool $isNameEmpty
 * @property-read bool $isNameNull
 * @property-read int $count
 * @property-read int $randomInt
 */
class Sample2
{
    /** @var string $name */
    private $name;
    
    /** @var int $time Unix timestamp when $this is created */
    private $time;
    
    public function __construct($name)
    {
        $this->name = (string)$name;
        $this->time = time();
    }
    
    // Define __get manually...
    public function __get($name)
    {
        switch ($name) {
            case 'name':
                return $this->name;
            case 'altName':
                return $this->name;
            case 'time':
                return $this->time;
            case 'isNameEmpty':
                return empty($this->name);
            case 'isNameNull':
                return $this->isNameNull();
            case 'count':
                return self::countUp();
            case 'randomInt':
                return rand();
            default:
                break;
        }
    }

    /** @return bool indicates $this->name is null */
    private function isNameNull()
    {
        return $this->name === null;
    }

    /** @return int number that is incremented on each call */
    private static function countUp()
    {
        static $counter = 0;
        return $counter++;
    }
}