三元运营商（猫王运营商）？：

我只是想知道为什么这个代码返回1

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

而如果我尝试这一个

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

和这个

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

他们都返回'complete'

基于这个？：运算符（'Elvis运算符'）在PHP中

他们都不应该返回相同的价值吗？

---

这是因为您在第一个示例中进行了布尔检查：

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

操作员告诉，如果陈述是真实的，则返回陈述的值，否则返回“不完整”。 所以它确实如此。 并且true值表示为1 。

你的例子解释了：

// 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';
}

---

你可以这样使用Elvis Operator：

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

在你的代码中你有这样一个声明：

$completed = true ?: 'Not Complete';

因此它返回true。

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