三值算子(猫王算子)

Question

我只是想知道为什么这段代码会返回1

$complete = 'complete';
$completed = ($complete == 'complete') ?: 'Not Complete';

如果我试试这个

$complete = 'complete';
$completed = ($complete == 'complete') ? $complete : 'Not Complete';

还有这张

$complete = 'complete';
if ($complete == 'complete') {
    $completed = $complete;
} else {
    $completed = 'Not Complete';
}

他们都会返回'complete'

基于这个?: operator (the 'Elvis operator') in PHP

难道它们不都应该返回相同的值吗？

Answer 1

这是因为在第一个示例中进行了布尔检查：

$complete == 'complete' // returns 'true'

运算符告诉，如果语句为true，则返回语句的值，否则返回“not”。所以确实如此。true表示为1。

你的例子解释如下：

// sets '$completed' to '($complete == 'complete')' what is 'true'
$completed = ($complete == 'complete') ?: 'Not Complete';

// sets '$completed' to '$completed', what is 'NULL', because '$completed' seems to be undefined before
$completed = ($complete == 'complete') ? $completed : 'Not Complete';

// sets '$completed' to the value of '$complete', because the statement is 'true'
if ($complete == 'complete') {
    $completed = $complete;
} else {
    $completed = 'Not Complete';
}

Answer 2

您可以这样使用Elvis操作符：

$completed = $complete ?: 'Not Complete';

在您的代码中，有一个类似于本例的语句：

$completed = true ?: 'Not Complete';

因此，它返回true。