How to Parse Basic Syntax in PHP Class Declarations?

Workaround for Basic Syntax Not Being Parsed

When parsing in PHP, discrepancies with basic syntax may occur. Specifically, assigning complex expressions as default values for class properties can be problematic.

While (1 << 0) is considered basic syntax, PHP disallows it in class declarations due to its nature as a verb that performs an action. Classes, as nouns, declare entities and should not evoke side effects like action statements. As a result, default values must be primitive.

To overcome this limitation, we propose a workaround that preserves readability and expandability:

1. Define Default Values Separately: Instead of inline expressions, define default values as constant arrays outside the class:

<code class="php">const STRING_NONE = 1 << 0;
const STRING_STRIP_COLOR = 1 << 1;</code>

2. Initialize Dynamically: Use a function to initialize class properties conditionally through dynamic expression evaluation:

<code class="php">class SDK
{
    // ...

    static protected $_types = null;

    static public function getType($type_name)
    {
        return self::$_types[$type_name] ?? throw new Exception("unknown type $type_name");
    }

    // ...

    function __construct($fString = null)
    {
        $fString = $fString ?: self::getType('STRING_NONE') & self::getType('STRING_HOSTS');
        // ...
    }
}</code>

This approach allows for clear separation of constant definitions and dynamic initialization, while maintaining flexibility in setting property values.

The above is the detailed content of How to Parse Basic Syntax in PHP Class Declarations?. For more information, please follow other related articles on the PHP Chinese website!