php - 空合并分配运算符如何发挥作用(How is Null Coalescing Assignment Operator doing any good)

Question

PHP 7.4 introduced Null coalescing assignment operator here's the RFC .

(PHP 7.4引入了Null合并赋值运算符，这里是RFC 。)

Here's the example for it:

(这是它的示例：)

// The folloving lines are doing the same
$this->request->data['comments']['user_id'] = $this->request->data['comments']['user_id'] ?? 'value';
// Instead of repeating variables with long names, the equal coalesce operator is used
$this->request->data['comments']['user_id'] ??= 'value';

As this seems reducing code repetition it's actually doing the opposite IMO, because in real life I would do this:

(由于这似乎减少了代码重复，实际上是在执行相反的IMO，因为在现实生活中，我会这样做：)

$id=$this->request->data['comments']['user_id'] ?? 'value';

Here I'm taking an advantage of copy-on-write policy in PHP.

(在这里，我利用了PHP中的写时复制策略 。)

Now I know that this will not change the data in the array ( which is good ) because if we do this:

(现在，我知道这不会更改数组中的数据（这是很好的），因为如果执行此操作：)

$this->request->data['comments']['user_id'] ??= 'value';

We will end up doing this :

(我们最终会这样做：)

$id = $this->request->data['comments']['user_id'];

Or this:

(或这个：)

echo $this->request->data['comments']['user_id'];

Which will lead to code repetition and also decreasing readability

(这将导致代码重复并降低可读性)

So again how is null coalescing assignment operator really useful?

(那么，空合并赋值运算符真的有用吗？)

  ask by FatalError translate from so

Answer 1

In PHP 7 this was originally released, allowing a developer to simplify an isset() check combined with a ternary operator.

(它最初是在PHP 7中发布的，它允许开发人员简化与三元运算符结合的isset（）检查。)

For example, before PHP 7, we might have this code:

(例如，在PHP 7之前，我们可能有以下代码：)

$data['username'] = (isset($data['username']) ? $data['username'] : 'guest');

When PHP 7 was released, we got the ability to instead write this as:

(当PHP 7发布时，我们可以改为这样写：)

$data['username'] = $data['username'] ?? 'guest';

Now, however, when PHP 7.4 gets released, this can be simplified even further into:

(但是，现在，当发布PHP 7.4时，可以进一步简化为：)

$data['username'] ??= 'guest';

One case where this doesn't work is if you're looking to assign a value to a different variable, so you'd be unable to use this new option.

(一种不起作用的情况是，如果您想为另一个变量分配值，那么您将无法使用此新选项。)

As such, while this is welcomed there might be a few limited use cases.

(因此，尽管这很受欢迎，但可能会有一些有限的用例。)