What do the square brackets in php mean?

Brackets ([]) are used in PHP for the following purposes: Array indexing: Gets or sets the value of an array element. Array declaration: declares an array containing elements. Hash table: declare key-value pairs (PHP 7.4). Scope parsing: parsing the scope of a variable or object. Mutable variable name: Create a variable containing the variable name.

The meaning of square brackets ([]) in PHP

The meaning of square brackets ([]) in PHP It has the following meanings:

1. Array index

• The square brackets are used to get or set the value of an element from an array. For example:

<code class="php">$array = ['apple', 'banana', 'cherry'];
echo $array[1]; // 输出：banana
$array[0] = 'grape';</code>

2. Array declaration

• Square brackets can also be used to declare arrays. For example:

<code class="php">$array = ['apple', 'banana', 'cherry'];</code>

3. Hash table (key-value pair)

• In PHP 7.4 and higher, square brackets can be used To declare a hash table (key-value pairs). Keys must be strings and values ​​can be of any data type. For example:

<code class="php">$hashTable = ['name' => 'John Doe', 'age' => 30];
echo $hashTable['name']; // 输出：John Doe</code>

4. Range parsing operator

• Square brackets can be used to parse the scope of a variable or object. For example:

<code class="php">class MyClass {
    public $name = 'John Doe';
}

$object = new MyClass();
echo $object->{$name}; // 输出：John Doe</code>

5. Variable variable name

• Square brackets can be used to create variable variables (that is, variables of variable names). For example:

<code class="php">$name = 'age';
$$name = 30;
echo $age; // 输出：30</code>

Note:

• Square brackets ([]) and curly brackets ({}) have different meanings in PHP. Curly braces are primarily used for control structures (for example, if, for, while) and objects.

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