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【PHP】类设计原则SOLID (object-oriented

2018-04-23  本文已影响28人  10xjzheng

原文: S.O.L.I.D: The First 5 Principles of Object Oriented Design

译者：10xjzheng

1.单一职责 Single responsibility principle

class Circle {
    public $radius;

    public function __construct($radius) {
        $this->radius = $radius;
    }
}

class Square {
    public $length;

    public function __construct($length) {
        $this->length = $length;
    }
}

class AreaCalculator {

    protected $shapes;

    public function __construct($shapes = array()) {
        $this->shapes = $shapes;
    }

    public function sum() {
        // logic to sum the areas
    }

    public function output() {
        return implode('', array(
            "",
                "Sum of the areas of provided shapes: ",
                $this->sum(),
            ""
        ));
    }
}

业务代码

$shapes = array(
    new Circle(2),
    new Square(5),
    new Square(6)
);

$areas = new AreaCalculator($shapes);

echo $areas->output();

业务代码应该是这样，即增加一个类SumCalculatorOutputter专门处理输出：

$shapes = array(
    new Circle(2),
    new Square(5),
    new Square(6)
);

$areas = new AreaCalculator($shapes);
$output = new SumCalculatorOutputter($areas);

echo $output->JSON();
echo $output->HAML();
echo $output->HTML();
echo $output->JADE();

2. 开闭原则 Open-closed Principle

public function sum() {
    foreach($this->shapes as $shape) {
        if(is_a($shape, 'Square')) {
            $area[] = pow($shape->length, 2);
        } else if(is_a($shape, 'Circle')) {
            $area[] = pi() * pow($shape->radius, 2);
        }
    }

    return array_sum($area);
}

修改后是这样的：

class Square {
    public $length;

    public function __construct($length) {
        $this->length = $length;
    }

    public function area() {
        return pow($this->length, 2);
    }
}   

public function sum() {
    foreach($this->shapes as $shape) {
        $area[] = $shape->area();
    }

    return array_sum($area);
}

interface ShapeInterface {
    public function area();
}

class Circle implements ShapeInterface {
    public $radius;

    public function __construct($radius) {
        $this->radius = $radius;
    }

    public function area() {
        return pi() * pow($this->radius, 2);
    }
}  

public function sum() {
    foreach($this->shapes as $shape) {
        if(is_a($shape, 'ShapeInterface')) {
            $area[] = $shape->area();
            continue;
        }

        throw new AreaCalculatorInvalidShapeException;
    }

    return array_sum($area);
}

3. 里氏替换原则 Liskov substitution principle

class VolumeCalculator extends AreaCalulator {
    public function __construct($shapes = array()) {
        parent::__construct($shapes);
    }

    public function sum() {
        // logic to calculate the volumes and then return and array of output
        return array($summedData);
    }
}

In the SumCalculatorOutputter class:

class SumCalculatorOutputter {
    protected $calculator;

    public function __constructor(AreaCalculator $calculator) {
        $this->calculator = $calculator;
    }

    public function JSON() {
        $data = array(
            'sum' => $this->calculator->sum();
        );

        return json_encode($data);
    }

    public function HTML() {
        return implode('', array(
            '',
                'Sum of the areas of provided shapes: ',
                $this->calculator->sum(),
            ''
        ));
    }
}

测试代码：

$areas = new AreaCalculator($shapes);
$volumes = new AreaCalculator($solidShapes);

$output = new SumCalculatorOutputter($areas);
$output2 = new SumCalculatorOutputter($volumes);

public function sum() {
    // logic to calculate the volumes and then return and array of output
    return $summedData;
}

4. 接口隔离原则 Interface segregation principle

interface ShapeInterface {
    public function area();
    public function volume();
}   

interface ShapeInterface {
    public function area();
}

interface SolidShapeInterface {
    public function volume();
}

class Cuboid implements ShapeInterface, SolidShapeInterface {
    public function area() {
        // calculate the surface area of the cuboid
    }

    public function volume() {
        // calculate the volume of the cuboid
    }
}

interface ManageShapeInterface {
    public function calculate();
}

class Square implements ShapeInterface, ManageShapeInterface {
    public function area() { /*Do stuff here*/ }

    public function calculate() {
        return $this->area();
    }
}

class Cuboid implements ShapeInterface, SolidShapeInterface, ManageShapeInterface {
    public function area() { /*Do stuff here*/ }
    public function volume() { /*Do stuff here*/ }

    public function calculate() {
        return $this->area() + $this->volume();
    }
}

5. 依赖反转原则 Dependency Inversion principle


class PasswordReminder {
    private $dbConnection;

    public function __construct(MySQLConnection $dbConnection) {
        $this->dbConnection = $dbConnection;
    }
}

interface DBConnectionInterface {
    public function connect();
}    

class MySQLConnection implements DBConnectionInterface {
    public function connect() {
        return "Database connection";
    }
}

class PasswordReminder {
    private $dbConnection;

    public function __construct(DBConnectionInterface $dbConnection) {
        $this->dbConnection = $dbConnection;
    }
}

Conclusion

Honestly, S.O.L.I.D might seem to be a handful at first, but with continuous usage and adherence to its guidelines, it becomes a part of you and your code which can easily be extended, modified, tested, and refactored without any problems.

实话说，solid原则看起来挺简单的，但坚持不懈地贯穿它的指导方针，它将会成为你代码的一部分，它将让你的代码更容易扩展，修改，测试，重构。

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