问题描述
我一直在尝试在 PHP 中更多地使用类型提示.今天我正在编写一个带有默认参数的布尔函数，我注意到表单的函数
I've been trying to use type hinting more in PHP. Today I was writing a function that takes a boolean with a default parameter and I noticed that a function of the form
function foo(boolean $bar = false) {
var_dump($bar);
}
实际上抛出了一个致命错误:
actually throws a fatal error:
具有类类型提示的参数的默认值只能为 NULL
Default value for parameters with a class type hint can only be NULL
一个类似形式的函数
function foo(bool $bar = false) {
var_dump($bar);
}
没有.但是，两者都
var_dump((bool) $bar);
var_dump((boolean) $bar);
给出完全相同的输出
:boolean false
:boolean false
这是为什么?这是否类似于 Java 中的包装类?
Why is this? Is this similar to the wrapper classes in Java?
推荐答案
http://php.net/manual/en/functions.arguments.php#functions.arguments.type-declaration
警告
不支持上述标量类型的别名.相反，它们被视为类或接口名称.例如，使用 boolean 作为参数或返回类型将需要一个参数或返回值，它是类或接口 boolean 的实例，而不是 bool 类型:
Warning
Aliases for the above scalar types are not supported. Instead, they are treated as class or interface names. For example, using boolean as a parameter or return type will require an argument or return value that is an instanceof the class or interface boolean, rather than of type bool:
<?php
function test(boolean $param) {}
test(true);
?>
上面的例子会输出:
致命错误:未捕获的 TypeError:传递给 test() 的参数 1 必须是布尔值的实例，给定的布尔值
Fatal error: Uncaught TypeError: Argument 1 passed to test() must be an instance of boolean, boolean given
简而言之，boolean 是 bool 的别名，而别名在类型提示中不起作用.
使用真实"名称:bool
So in a nutshell, boolean is an alias for bool, and aliases don't work in type hints.
Use the "real" name: bool
类型提示之间没有相似之处 和 类型转换.
类型提示类似于你告诉你的函数应该接受哪种类型.
Type hinting is something like that you are telling your function which type should be accepted.
类型转换是在类型之间切换".
允许的演员表是:
(int), (integer) - cast to integer
(bool), (boolean) - cast to boolean
(float), (double), (real) - cast to float
(string) - cast to string
(array) - cast to array
(object) - cast to object
(unset) - cast to NULL (PHP 5)
在 php 中类型转换 (bool) 和 (boolean) 都是一样的.
In php type casting both (bool) and (boolean) are the same.
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