最近我在 PHP 代码中看到了这行：
$dbObject = json_decode($jsonString);
$dbObject->{'mysql-5.4'}[0]->credentials
但是如何定义对象$dbObject以允许方括号和花括号都可以互换使用来访问数组元素（例如，在上面的示例中，$array[42]和$array{42}将执行相同的操作）。
-> {...}[...]访问？这段代码是否有点不安全？哪个PHP版本支持此功能？它的作用是使得访问某些属性不再是裸字面量，从而避免无效语法。意思是：
$dbObject->mysql-5.4[0]->credentials
这是无效/不明确的语法。为了让PHP清楚mysql-5.4是一个属性而不是一个减去浮点数的属性，您需要使用{'..'}语法。
确切地说，->{..}使您可以将任何表达式用作属性名称。例如：
$dbObject->{ sprintf('%s-%.1f', 'mysql', 5.4) }
__get）。 - Luca Rainone(per @Deceze's answer): It allows you to access property names that would otherwise not be valid PHP syntax -- eg if the property name contains a dot or dash, per your example. Typically properties like this would be accessed via a __get() magic method, since they would also be invalid syntax to define as an actual property within the class.
(per @feela's answer): It allows you to use variables to reference your properties. This is similar to the $$ variable variable syntax. It's generally not really very good practice, but is useful in some cases.
(not mentioned by any other answers yet): It allows you to remove certain potential ambiguities from your code. Consider the following code for example:
$output = $foo->$bar['baz'];
This is ambiguous. You can resolve the ambiguity by adding braces or brackets:
$output = $foo->{$bar['baz']}; //gets the value of a property from $foo which has a name that is defined in $bar['baz']
$output = ($foo->$bar)['baz']; //gets the ['baz'] element of $foo->$bar array.
This is particularly important because the forthcoming relese of PHP 7 will change the default behaviour of code like like. This will make the language behave more consistently, but will break existing code that doesn't have the braces.
See also the PHP documentation for this change here: https://wiki.php.net/rfc/uniform_variable_syntax
But even without the language change to force the issue, code like this should have braces anyway to help with readability -- if you don't put braces, then you may end up struggling to work out what you were trying to do when you come back to the code in six months' time.
echo $foo->{$baz[1]} . "\n";
echo $foo->{$start . $end} . "\n";
echo $foo->{$arr[1]} . "\n";
->运算符意味着您正在访问对象属性。 在这种情况下，属性名称应该是mysql-5.4，它不是有效的PHP标识符（它必须包含字母，数字或下划线，请参见here）。 因此可以100％确定属性名称已经动态创建。__get()的魔术方法重载属性。 此方法的主体允许您处理任何属性 - 这可以是任何字符串，任何变量，甚至是一个强制转换为字符串的对象。__get()魔术方法处理字符串mysql-5.4。 大括号{和}用于表示该字符串应被视为属性名称（但是没有具有此名称的属性）。大多数情况下，在->{后面会有一个$，就像->$variable。
例如，我们有：
$languageCode = 'en';
$obj->{$languageCode};
$obj->{$languageCode}等同于$obj->en
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在您的情况下，这是因为在php中不允许这样写：
$dbObject->mysql-5.4
$dbObject->{'mysql-5.4'}[0]->credentials
$dbObject->{'mysql-5.4'}[0]->credentials？ - WeSee{"mysql-5.4":[{"credentials":1}]}пј€е°†1ж›їжЌўдёє$dbObject->{'mysql-5.4'}[0]->credentialsзљ„еЂјпј‰гЂ‚ - Michael