How can PHP developers avoid issues with variable types when passing data between functions in a class?

PHP developers can avoid issues with variable types when passing data between functions in a class by explicitly defining the data types of parameters and return values in function signatures. This ensures that the functions only accept and return the expected data types, reducing the risk of type mismatches or errors. Additionally, using type hinting and type checking within the functions can help catch and handle any unexpected data types.

class MyClass {
    public function processData(int $num): string {
        // process the integer data and return a string
        return "Processed data: " . $num;
    }

    public function displayData(string $data): void {
        // display the processed data
        echo $data;
    }
}

// Example usage
$myObject = new MyClass();
$data = $myObject->processData(42);
$myObject->displayData($data);