PHP7：具有标量类型声明的方法拒绝键入杂耍 NULL 值，即使在 weak/coercive 模式下也是如此

Question

截至 PHP 7.0, the scalar type hints int, float, string, and bool can be included in method signatures. By default, these type declarations operate in weak/coercive mode (or "type juggling" mode). According to the PHP manual：

PHP will coerce values of the wrong type into the expected scalar type if possible. For example, a function that is given an integer for a parameter that expects a string will get a variable of type string.

但是即使可以将 NULL 强制转换为整数 0，具有 int 类型提示的方法将拒绝强制转换为 [=18 的入站值=] 到整数 0.

<?php

class MyClass
{
    public function test(int $arg)
    {
        echo $arg;
    }
}

$obj = new MyClass();
$obj->test('123'); // 123
$obj->test(false); // 0
$obj->test(null);  // TypeError: Argument 1 passed to MyClass::test()
                   // must be of the type integer, null given

同样，即使 it is possible 将 NULL 强制转换为布尔值 false，具有 bool 类型提示的方法将拒绝将 NULL 的入站值强制转换为布尔值 false。 float 和 string 类型提示也是如此。

此行为似乎与 php.net 上的文档相矛盾。这是怎么回事？

Answer 1

目前没有办法允许带有标量类型提示的方法自动输入杂耍 声明类型的入站 NULL 值.

根据 RFC 负责将此功能引入 PHP 7:

The weak type checking rules for the new scalar type declarations are mostly (emphasis added) the same as those of extension and built-in PHP functions. The only exception to this is the handling of NULL: in order to be consistent with our existing type declarations for classes, callables and arrays, NULL is not accepted by default, unless it is a parameter and is explicitly given a default value of NULL.

但是，在以下情况下，NULL 值可以被接受为 NULL：

<?php

class MyClass
{
    // PHP 7.0+
    public function testA(int $arg = null)
    {
        if (null === $arg) {
            echo 'The argument is NULL!';
        }
    }

    // PHP 7.1+
    // https://wiki.php.net/rfc/nullable_types
    public function testB(?int $arg)
    {
        if (null === $arg) {
            echo 'The argument is NULL!';
        }
    }
}

$obj = new MyClass();
$obj->testA(null); // The argument is NULL!
$obj->testB(null); // The argument is NULL!

PHP7：具有标量类型声明的方法拒绝键入杂耍 NULL 值，即使在 weak/coercive 模式下也是如此

PHP7: Methods with a scalar type declaration refuse to type juggle NULL values, even in weak/coercive mode

php

casting

type-hinting

php-7