属性默认值null是否等于没有默认值? [英] Is a property default value of null the same as no default value?
问题描述
因此,我可以安全地重构
And can I therefore safely refactor all instances of
class Blah
{
// ...
private $foo = null;
// ...
}
to
class Blah
{
// ...
private $foo;
// ...
}
?
推荐答案
未键入的属性
简单的答案,是的。参见 http://php.net/manual/en/language.types.null .php
特殊的NULL值表示没有值的变量。 NULL是
唯一可能为null类型的值。
The special NULL value represents a variable with no value. NULL is the only possible value of type null.
您可以通过执行 var_dump()
上的属性,您将看到两个实例均为 NULL
You can easily test by performing a var_dump()
on the property and you will see both instances it will be NULL
class Blah1
{
private $foo;
function test()
{
var_dump($this->foo);
}
}
$test1 = new Blah1();
$test1->test(); // Outputs NULL
class Blah2
{
private $foo = NULL;
function test()
{
var_dump($this->foo);
}
}
$test2 = new Blah2();
$test2->test(); // Outputs NULL
类型化属性
PHP 7.4添加了类型化属性默认情况下,如无类型属性一样,默认为 null
,而是默认为特殊的未初始化状态,如果在写入属性之前先读取该属性,则会导致错误。参见类型声明。
Typed properties
PHP 7.4 adds typed properties which do not default to null
by default like untyped properties, but instead default to a special "uninitialised" state which will cause an error if the property is read before it is written. See the "Type declarations" section on the PHP docs for properties.
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