if (!$conditions = $this->input->post()) {
// Single equal sign in an if condition: make assignment, and check
// whether the result is truthy.
$conditions = array('tutor' => $this->session->userdata('user_id'));
}
这是我自己的代码中相当常见的模式。这只会执行函数 $this->input->post() 一次。如果结果为真，则该结果存储在 $conditions 中。如果结果不为真，则运行 if 条件内的代码。这会将回退值分配给 $conditions。好处是，无论哪种情况，$this->input->post() 仅运行一次。
The accepted answer is correct, but misses one important point:
$x = $a ? : $b; // valid in PHP 5.3
should indeed be replaced with
$x = $a ? $a : $b; // valid in older versions of PHP
However, when you're dealing with functions, not variables, be aware of side-effects:
In the above case, if $this->input->post()returns a truthy value, the function will be executed again, which may not be what you want. You can see this more clearly by expanding the ternary operator to its full form:
You can see that the function is executed on lines one and two above. If you don't want that, try this instead:
if (!$conditions = $this->input->post()) {
// Single equal sign in an if condition: make assignment, and check
// whether the result is truthy.
$conditions = array('tutor' => $this->session->userdata('user_id'));
}
This is a fairly common pattern in my own code. This will execute the function $this->input->post() only once. If the result is truthy, that result is stored in $conditions. If the result is not truthy, the code inside the if condition is run. This assigns the fallback value to $conditions. The benefit is that, in either case, $this->input->post() is run only once.
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评论（3）
三元运算符（顾名思义）通常需要 3 个参数，
在 PHP5.3 中允许省略
$trueValue。在这种情况下，它的$expr用于它您的服务器上可能没有 PHP5.3。正如您在我的示例中看到的，修复此问题并为 5.3 之前的版本做好准备非常容易
The ternary operator (as the name suggests) usually expects 3 arguments
With PHP5.3 its allowed to omit
$trueValue. In this case its$expris used for itYou probably don't have PHP5.3 on your server. As you can see in my example its quite easy to fix this and make it ready for pre-5.3
语法
? :您使用的只是 PHP 5.3。设置默认值：
The syntax
? :you are using is PHP 5.3 only.Set a default value:
接受的答案是正确的，但忽略了一个重要的一点：
确实应该替换为
但是，当您处理函数时，而不是变量，请注意副作用：
在上面的情况下，如果
$this->input->post()返回一个真值，该函数将再次执行，这可能不是你想要什么。通过将三元运算符展开为其完整形式，您可以更清楚地看到这一点：您可以看到该函数在上面的第一行和第二行执行。如果您不想这样做，请尝试以下操作：
这是我自己的代码中相当常见的模式。这只会执行函数
$this->input->post()一次。如果结果为真，则该结果存储在$conditions中。如果结果不为真，则运行if条件内的代码。这会将回退值分配给$conditions。好处是，无论哪种情况，$this->input->post()仅运行一次。The accepted answer is correct, but misses one important point:
should indeed be replaced with
However, when you're dealing with functions, not variables, be aware of side-effects:
In the above case, if
$this->input->post()returns a truthy value, the function will be executed again, which may not be what you want. You can see this more clearly by expanding the ternary operator to its full form:You can see that the function is executed on lines one and two above. If you don't want that, try this instead:
This is a fairly common pattern in my own code. This will execute the function
$this->input->post()only once. If the result is truthy, that result is stored in$conditions. If the result is not truthy, the code inside theifcondition is run. This assigns the fallback value to$conditions. The benefit is that, in either case,$this->input->post()is run only once.