在PHP中将函数实现为对象

$add = function($a, $b) {
    return $a + $b;
};

echo $add(2, 3); // 输出 5

function calculate($a, $b, $operation) {
    return $operation($a, $b);
}

$result = calculate(2, 3, function($a, $b) {
    return $a + $b;
});

echo $result; // 输出 5

class Calculator {
    private $operation;

    public function setOperation($operation) {
        $this->operation = $operation;
    }

    public function calculate($a, $b) {
        return $this->operation->__invoke($a, $b);
    }
}

$calculator = new Calculator();
$calculator->setOperation(function($a, $b) {
    return $a + $b;
});

echo $calculator->calculate(2, 3); // 输出 5