Why can\'t you initialize a PHP class property to a function at declaration time?

Why Can't You Initialize a PHP Property to a Function?

When attempting to initialize a PHP class property to a function during its declaration, a "Parse error: syntax error, unexpected T_FUNCTION" error may arise.

<code class="php">class AssignAnonFunction {
    private $someFunc = function() {
        echo "Will Not work";
    };
}</code>

This occurs because PHP does not allow properties to be initialized with non-constant values, such as functions. The PHP manual explains:

"Properties are defined by using one of the keywords public, protected, or private, followed by a normal variable declaration... this initialization must be a constant value... it must be able to be evaluated at compile time and must not depend on run-time information in order to be evaluated."

Therefore, functions cannot be assigned to properties at declaration time.

However, properties can be initialized with functions using the __construct() method:

<code class="php">class AssignAnonFunctionInConstructor {
    private $someFunc;

    public function __construct() {
        $this->someFunc = function() {
            echo "Does Work";
        };
    }
}</code>

This is possible because the __construct() method is called at runtime, allowing for the assignment of dynamic values, including functions.

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