class Calculator {
    PRivate $_val1,$_val2;

    public function __construct($val1,$val2){
        $this->_val1 = $val1;
        $this->_val2 = $val2;
    }

    public function add(){
        return $this->_val1 + $this->_val2;
    }

    public function suBTract(){
        return $this->_val1 - $this->_val2;
    }

    public function multiply (){
        return $this->_val1 * $this->_val2;
    }

    public function divide () {
        return $this->_val1 / $this->_val2;
    }
}

$calc = new Calculator(3,4);
echo "<p>3 + 4 = ".$calc->add(). "</p>";

$calc = new Calculator (15,12);
echo "<p>15 - 12 = ".$calc->subtract(). "</p>";

$calc = new Calculator (20,2);
echo "<p> 20 * 2 = ".$calc->;multiply(). "</p>";

$calc = new Calculator (20,2);
echo "<p> 20 / 2 = ".$calc ->divide(). "</p>";

恕我直言,你应该使用多态性.
This Video可以帮助您理解这一原则

这是我的思维方式.

首先,为您需要的任何操作定义接口

interface operationInterface
{
    public function evaluate(array $oPErands = array());
}

然后,创建计算器支架

class Calculator
{
    protected $operands = array();

    public function setOperands(array $operands = array())
    {
        $this->operands = $operands;
    }

    public function addOperand($operand)
    {
        $this->operands[] = $operand;
    }

    /**
     * You need any operation that implement the given interface
     */
    public function setOperation(OperationInterface $operation)
    {
        $this->operation = $operation;
    }

    public function process()
    {
        return $this->operation->evaluate($this->operands);
    }
}

然后,您可以定义操作,例如,添加

class AddITion implements OperationInterface
{
    public function evaluate(array $operands = array())
    {
        return array_sum($operands);
    }
}

你会像以下一样使用它：

$calculator = new Calculator;
$calculator->setOperands(array(4,2));
$calculator->setOperation(new Addition);

echo $calculator->process(); // 6

有了这一点,如果要添加任何新行为或修改现有行为,只需创建或编辑一个类.

例如,假设您需要模数运算

class Modulus implements OperationInterface
{
    public function evaluate(array $operands = array())
    {
        $equals = array_shift($operands);

        foreach ($operands as $value) {
            $equals = $equals % $value;
        }

        return $equals;
    }
}

然后,

$calculator = new Calculator;
$calculator->setOperands(array(4,2));
$calculator->setOperation(new Addition); // 4 + 2

echo $calculator->process(); // 6

$calculator->setOperation(new Modulus); // 4 % 2

echo $calculator->process(); // 0

$calculator->setOperands(array(55,10)); // 55 % 10

echo $calculator->process(); // 5

此解决方案允许您的代码成为第三方库

如果您计划重用此代码或将其作为库提供,则用户不会修改您的源代码.
但是,如果他想要一个未定义的Substraction或Backwardsubstraction方法呢？

他只需要在他的项目中创建自己的Substraction类,它实现OperationInterface以便与你的库一起工作.

它更容易阅读

在查看项目架构时,更容易看到这样的文件夹

- app/
    - lib/
        - Calculator/
            - Operation/
                - Addition.PHP
                - Modulus.PHP
                - Substraction.PHP
            - OperationInterface.PHP
            - Calculator.PHP

并立即知道哪个文件包含所需的行为.