问题描述
我只是感觉在方法类型提示中使用问号的php(symfony/laravel)代码片段:
I just felt on pieces of php (symfony/laravel) code using question mark in method type hints :
public function functionName(?int $arg = 0)
在其他情况下，?类型不是最后一个，但是我没有找到其中的任何一个，但都没有默认值.
In other occasions the ?type was not the last one, but I did not find any of these with no default yet.
问题是，我找不到有关此的任何信息，所以我检查了:
Problem is, I cannot find any information about this, and I checked :
- 此处: http://php.net/manual/en/migration70. new-features.php
- 以及此处: http://php.net/manual/zh/migration71 .new-features.php
- 以及此处: http://php.net/manual/zh/functions.arguments .php
- here : http://php.net/manual/en/migration70.new-features.php
- and here : http://php.net/manual/en/migration71.new-features.php
- and here : http://php.net/manual/en/functions.arguments.php
与7.2相同，但是由于代码仅需要7.1，所以看起来很正常.
And same with 7.2, but since the code only requires 7.1, it seems rather normal.
我也谷歌搜索并在这里搜索，但是要么没有记录在案，要么问号主题正在击败搜索引擎.
I also googled, and searched here, but either this is not documented or the question marks topic is defeating search engines.
所以我现在有点傻了，如果有人能在方法签名参数中启发我这个问号的含义，我将不胜感激.
So I feel a little dumb now, and I would really appreciate if someone could enlighten me on the signification of this question mark in method signatures arguments.
谢谢
推荐答案
这是php7.1中的新功能
It's a new feature in php7.1
http://php.net/manual/en/migration71.new- features.php
问号表示类型提示参数(或返回值)也可以为空.
A question mark means that the type hinted parameter (or return value) is also allowed to be null.
因此在您的示例中，$ arg可以为null或任何整数.
So in your example $arg can be null or any integer.
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