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                **一.聯合類型作用** 低版本只能為屬性、參數和返回類型聲明單個類型。PHP7.1支持了null類型,但已被PHP8中的?代替. ``` string|null $name ?string $name ``` &emsp; **二.類型** 1.屬性 ``` class Person{ public string $name; public function __construct(public string|array $name){ var_dump($this->name); } } new Person([]); ``` 2.參數 ``` function show(int|string $a){ var_dump($a); } show('yzmedu'); ``` 3.返回類型 ``` function show(int|string $a):int|string{ var_dump($a); return 5; } echo show('yzmedu'); ``` &emsp; **三.類型約束** 1.舊版本一種形式約束 ``` /** * @a int|string */ function show($a){ echo $a; } show('yzmedu'); ``` 2.強制約束 ``` #[show(a,'int','string')] function show(int|string $a){ echo $a; } show('yzmedu'); ``` &emsp; **四.void不允許與其他任何類型組合,棄用** ``` function foo(): void|null {} ``` &emsp; **五.?和null類型** 1.單類型建議使用? ``` function show(?string $a){ var_dump($a); } show(null); function show(string|null $a){ var_dump($a); } show(null); ``` 2.多類型只能使用null ``` function show(int|string|null $a){ var_dump($a); } show(null); ``` &emsp; **六.不允許使用冗余類型** ``` function show(bool|false $name){ var_dump($name); } show(true); ``` &emsp; ### **系統的學習PHP** 關注:PHP自學中心,回復相應的關鍵詞,領取以下視頻教程 **PHP開發API接口視頻教程** 公眾號里回復:637939 &emsp; #### **還有其他的教程的關鍵詞,請關注公眾號查看每天分享的文章教程的頭部** ![](https://img.kancloud.cn/96/af/96af322d2cdc53d3fbbe981affa60c7f_150x150.jpg)
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