PHP 5.6

class BlogData{    /** @var string */
    private $title;    
    /** @var State */
    private $state;    
    /** @var \DateTimeImmutable|null */
    private $publishedAt;   
   /**
    * @param string $title 
    * @param State $state 
    * @param \DateTimeImmutable|null $publishedAt 
    */
    public function __construct($title,$state,$publishedAt = null) {        
                $this->title = $title;        
                $this->state = $state;        
                $this->publishedAt = $publishedAt;
    }    
    /**
     * @return string 
     */
    public function getTitle(){        
                return $this->title;    
    }    
    /**
     * @return State 
     */
    public function getState() 
    {        
                return $this->state;    
    }    
    /**
     * @return \DateTimeImmutable|null 
     */
    public function getPublishedAt() 
    {        
                return $this->publishedAt;    
    }
}

php7 引入 标量类型和返回类型

class BlogData{    /** @var string */
    private $title;    
    /** @var State */
    private $state;    
    /** @var \DateTimeImmutable|null */
    private $publishedAt;   
   /**
    * @param \DateTimeImmutable|null $publishedAt 
    */
    public function __construct(string $title,State $state,$publishedAt = null) {        
            $this->title = $title;        
            $this->state = $state;        
            $this->publishedAt = $publishedAt;
    }    
    public function getTitle(): string
    {        
            return $this->title;    
    }    
    public function getState(): State 
    {        
            return $this->state;    
    }    
    /**
     * @return \DateTimeImmutable|null 
     */
    public function getPublishedAt() 
    {        
            return $this->publishedAt;    
    }
}

PHP 7.1 终于出现了可以为空的类型

class BlogData{    /** @var string */
    private $title;    
    /** @var State */
    private $state;    
    /** @var \DateTimeImmutable|null */
    private $publishedAt;   
    public function __construct(
        string $title,
        State $state,
        ?DateTimeImmutable $publishedAt = null) {        
            $this->title = $title;        
            $this->state = $state;        
            $this->publishedAt = $publishedAt;
    }    
    public function getTitle(): string
    {        
            return $this->title;    
    }    
    public function getState(): State 
    {        
            return $this->state;    
    }    
    public function getPublishedAt(): ?DateTimeImmutable
    {        
            return $this->publishedAt;    
    }
}

PHP 7.4 类型化属性

class BlogData{    private string $title;    
    private State $state;    
    private ?DateTimeImmutable $publishedAt;   
    public function __construct(
        string $title,
        State $state,
        ?DateTimeImmutable $publishedAt = null) {        
            $this->title = $title;        
            $this->state = $state;        
            $this->publishedAt = $publishedAt;
    }    
    public function getTitle(): string
    {        
            return $this->title;    
    }    
    public function getState(): State 
    {        
            return $this->state;    
    }    
    public function getPublishedAt(): ?DateTimeImmutable
    {        
            return $this->publishedAt;    
    }
}

PHP 8.0 增加了提升属性

class BlogData{    public function __construct(
        private string $title,        
                private State $state,        
                private ?DateTimeImmutable $publishedAt = null, ){}    
    public function getTitle(): string
    {        
                return $this->title;    
    }    
    public function getState(): State 
    {        
                return $this->state;    
    }    
    public function getPublishedAt(): ?DateTimeImmutable
    {        
                return $this->publishedAt;    
    }
}

php8.1  只读属性

class BlogData{    
    public function __construct(
        public readonly string $title,        
        public readonly State $state,        
        public readonly ?DateTimeImmutable $publishedAt = null,) {}
}

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