How to Assign Anonymous Functions to Class Properties in PHP?

Assigning Anonymous Functions to Class Properties in PHP

In PHP, it is not possible to directly initialize a class property to an anonymous function when declaring it. The code snippet below:

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

Generates the error message "Parse error: syntax error, unexpected T_FUNCTION." This is because the PHP language does not allow the initialization of properties with functions during the declaration phase.

Constant Value Initialization Restriction

According to the PHP manual, class properties can only be initialized with constant values during their declaration. A constant value is one that can be evaluated at compile time without relying on runtime information. Functions, however, do not fit this criterion and are therefore not allowed as property initializers during declaration.

Workaround Using Constructor

Despite the inability to initialize properties with anonymous functions during declaration, it is possible to assign functions to properties within the constructor method. Modifying the previous code to the following allows for the assignment:

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

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

The constructor method is called upon object creation, allowing for the assignment of the anonymous function to the property at runtime.

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