class Email
{
//...
public function handle(): void
{
mail($this->to, $this->subject, $this->body);
}
}
$message = new Email(...);
// What is this? A handle for the message? Are we writing to a file now?
$message->handle();
很好的例子:
class Email
{
//...
public function send(): void
{
mail($this->to, $this->subject, $this->body);
}
}
$message = new Email(...);
// Clear and obvious
$message->send();
class DBConnection
{
private static $instance;
private function __construct(string $dsn)
{
// ...
}
public static function getInstance(): DBConnection
{
if (self::$instance === null) {
self::$instance = new self();
}
return self::$instance;
}
// ...
}
$singleton = DBConnection::getInstance();
好的示范：
class DBConnection
{
public function __construct(string $dsn)
{
// ...
}
// ...
}
用 DSN 进行配置创建的 DBConnection 类实例。
$connection = new DBConnection($dsn);
现在就必须在你的应用中使用 DBConnection 的实例了。 封装条件语句
不友好的:
if ($article->state === 'published') {
// ...
}
友好的:
if ($article->isPublished()) {
// ...
}
避免用反义条件判断
不友好的:
function isDOMNodeNotPresent(\DOMNode $node): bool
{
// ...
}
if (!isDOMNodeNotPresent($node))
{
// ...
}
友好的:
function isDOMNodePresent(\DOMNode $node): bool
{
// ...
}
if (isDOMNodePresent($node)) {
// ...
}
避免使用条件语句
这听起来像是个不可能实现的任务。 当第一次听到这个时，大部分人都会说，“没有 if 语句，我该怎么办？” 答案就是在很多情况下你可以使用多态性来实现同样的任务。 接着第二个问题来了， “听着不错，但我为什么需要那样做？”，这个答案就是我们之前所学的干净代码概念：一个函数应该只做一件事情。如果你的类或函数有 if 语句，这就告诉了使用者你的类或函数干了不止一件事情。 记住，只要做一件事情。
不好的:
class Airplane
{
// ...
public function getCruisingAltitude(): int
{
switch ($this->type) {
case '777':
return $this->getMaxAltitude() - $this->getPassengerCount();
case 'Air Force One':
return $this->getMaxAltitude();
case 'Cessna':
return $this->getMaxAltitude() - $this->getFuelExpenditure();
}
}
}
好的:
interface Airplane
{
// ...
public function getCruisingAltitude(): int;
}
class Boeing777 implements Airplane
{
// ...
public function getCruisingAltitude(): int
{
return $this->getMaxAltitude() - $this->getPassengerCount();
}
}
class AirForceOne implements Airplane
{
// ...
public function getCruisingAltitude(): int
{
return $this->getMaxAltitude();
}
}
class Cessna implements Airplane
{
// ...
public function getCruisingAltitude(): int
{
return $this->getMaxAltitude() - $this->getFuelExpenditure();
}
}
function combine($val1, $val2): int
{
if (!is_numeric($val1) || !is_numeric($val2)) {
throw new \Exception('Must be of type Number');
}
return $val1 + $val2;
}
好的：
function combine(int $val1, int $val2): int
{
return $val1 + $val2;
}
class BankAccount
{
public $balance = 1000;
}
$bankAccount = new BankAccount();
// Buy shoes...
$bankAccount->balance -= 100;
好的:
class BankAccount
{
private $balance;
public function __construct(int $balance = 1000)
{
$this->balance = $balance;
}
public function withdraw(int $amount): void
{
if ($amount > $this->balance) {
throw new \Exception('Amount greater than available balance.');
}
$this->balance -= $amount;
}
public function deposit(int $amount): void
{
$this->balance += $amount;
}
public function getBalance(): int
{
return $this->balance;
}
}
$bankAccount = new BankAccount();
// Buy shoes...
$bankAccount->withdraw($shoesPrice);
// Get balance
$balance = $bankAccount->getBalance();
让对象拥有 private/protected 属性的成员
public 公有方法和属性对于变化来说是最危险的，因为一些外部的代码可能会轻易的依赖他们，但是你没法控制那些依赖他们的代码。 类的变化对于类的所有使用者来说都是危险的。
protected 受保护的属性变化和 public 公有的同样危险，因为他们在子类范围内是可用的。也就是说 public 和 protected 之间的区别仅仅在于访问机制，只有封装才能保证属性是一致的。任何在类内的变化对于所有继承子类来说都是危险的 。
class Employee
{
public $name;
public function __construct(string $name)
{
$this->name = $name;
}
}
$employee = new Employee('John Doe');
echo 'Employee name: '.$employee->name; // Employee name: John Doe
Good:
class Employee
{
private $name;
public function __construct(string $name)
{
$this->name = $name;
}
public function getName(): string
{
return $this->name;
}
}
$employee = new Employee('John Doe');
echo 'Employee name: '.$employee->getName(); // Employee name: John Doe
类 组合优于继承
正如 the Gang of Four 所著的 设计模式 中所说，
我们应该尽量优先选择组合而不是继承的方式。使用继承和组合都有很多好处。
这个准则的主要意义在于当你本能的使用继承时，试着思考一下组合是否能更好对你的需求建模。
在一些情况下，是这样的。
接下来你或许会想，“那我应该在什么时候使用继承？”
答案依赖于你的问题，当然下面有一些何时继承比组合更好的说明：
class UserSettings
{
private $user;
public function __construct(User $user)
{
$this->user = $user;
}
public function changeSettings(array $settings): void
{
if ($this->verifyCredentials()) {
// ...
}
}
private function verifyCredentials(): bool
{
// ...
}
}
棒棒哒:
class UserAuth
{
private $user;
public function __construct(User $user)
{
$this->user = $user;
}
public function verifyCredentials(): bool
{
// ...
}
}
class UserSettings
{
private $user;
private $auth;
public function __construct(User $user)
{
$this->user = $user;
$this->auth = new UserAuth($user);
}
public function changeSettings(array $settings): void
{
if ($this->auth->verifyCredentials()) {
// ...
}
}
}
abstract class Adapter
{
protected $name;
public function getName(): string
{
return $this->name;
}
}
class AjaxAdapter extends Adapter
{
public function __construct()
{
parent::__construct();
$this->name = 'ajaxAdapter';
}
}
class NodeAdapter extends Adapter
{
public function __construct()
{
parent::__construct();
$this->name = 'nodeAdapter';
}
}
class HttpRequester
{
private $adapter;
public function __construct(Adapter $adapter)
{
$this->adapter = $adapter;
}
public function fetch(string $url): Promise
{
$adapterName = $this->adapter->getName();
if ($adapterName === 'ajaxAdapter') {
return $this->makeAjaxCall($url);
} elseif ($adapterName === 'httpNodeAdapter') {
return $this->makeHttpCall($url);
}
}
private function makeAjaxCall(string $url): Promise
{
// request and return promise
}
private function makeHttpCall(string $url): Promise
{
// request and return promise
}
}
好的:
interface Adapter
{
public function request(string $url): Promise;
}
class AjaxAdapter implements Adapter
{
public function request(string $url): Promise
{
// request and return promise
}
}
class NodeAdapter implements Adapter
{
public function request(string $url): Promise
{
// request and return promise
}
}
class HttpRequester
{
private $adapter;
public function __construct(Adapter $adapter)
{
$this->adapter = $adapter;
}
public function fetch(string $url): Promise
{
return $this->adapter->request($url);
}
}
里氏代换原则 (LSP)
这是一个简单概念的可怕术语。它通常被定义为 “如果 S 是 T 的一个子类型，则 T 型对象可以替换为 S 型对象”
(i.e., S 类型的对象可以替换 T 型对象) 在不改变程序的任何理想属性的情况下 (正确性，任务完成度，etc.)." 这是一个更可怕的定义.
这个的最佳解释是，如果你有个父类和一个子类，然后父类和子类可以互换使用而不会得到不正确的结果。这或许依然令人疑惑，所以我们来看下经典的正方形 - 矩形例子。几何定义，正方形是矩形，但是，如果你通过继承建立了 “IS-a” 关系的模型，你很快就会陷入麻烦。.
不好的:
class Rectangle
{
protected $width = 0;
protected $height = 0;
public function render(int $area): void
{
// ...
}
public function setWidth(int $width): void
{
$this->width = $width;
}
public function setHeight(int $height): void
{
$this->height = $height;
}
public function getArea(): int
{
return $this->width * $this->height;
}
}
class Square extends Rectangle
{
public function setWidth(int $width): void
{
$this->width = $this->height = $width;
}
public function setHeight(int $height): void
{
$this->width = $this->height = $height;
}
}
/**
* @param Rectangle[] $rectangles
*/
function renderLargeRectangles(array $rectangles): void
{
foreach ($rectangles as $rectangle) {
$rectangle->setWidth(4);
$rectangle->setHeight(5);
$area = $rectangle->getArea(); // BAD: Will return 25 for Square. Should be 20.
$rectangle->render($area);
}
}
$rectangles = [new Rectangle(), new Rectangle(), new Square()];
renderLargeRectangles($rectangles);
优秀的:
abstract class Shape
{
abstract public function getArea(): int;
public function render(int $area): void
{
// ...
}
}
class Rectangle extends Shape
{
private $width;
private $height;
public function __construct(int $width, int $height)
{
$this->width = $width;
$this->height = $height;
}
public function getArea(): int
{
return $this->width * $this->height;
}
}
class Square extends Shape
{
private $length;
public function __construct(int $length)
{
$this->length = $length;
}
public function getArea(): int
{
return pow($this->length, 2);
}
}
/**
* @param Rectangle[] $rectangles
*/
function renderLargeRectangles(array $rectangles): void
{
foreach ($rectangles as $rectangle) {
$area = $rectangle->getArea();
$rectangle->render($area);
}
}
$shapes = [new Rectangle(4, 5), new Rectangle(4, 5), new Square(5)];
renderLargeRectangles($shapes);
interface Employee
{
public function work(): void;
public function eat(): void;
}
class Human implements Employee
{
public function work(): void
{
// ....working
}
public function eat(): void
{
// ...... eating in lunch break
}
}
class Robot implements Employee
{
public function work(): void
{
//.... working much more
}
public function eat(): void
{
//.... robot can't eat, but it must implement this method
}
}
好的:
并不是每个工人都是雇员，但每个雇员都是工人.
interface Workable
{
public function work(): void;
}
interface Feedable
{
public function eat(): void;
}
interface Employee extends Feedable, Workable
{
}
class Human implements Employee
{
public function work(): void
{
// ....working
}
public function eat(): void
{
//.... eating in lunch break
}
}
// robot can only work
class Robot implements Workable
{
public function work(): void
{
// ....working
}
}
class Employee
{
public function work(): void
{
// ....working
}
}
class Robot extends Employee
{
public function work(): void
{
//.... working much more
}
}
class Manager
{
private $employee;
public function __construct(Employee $employee)
{
$this->employee = $employee;
}
public function manage(): void
{
$this->employee->work();
}
}
优秀的:
interface Employee
{
public function work(): void;
}
class Human implements Employee
{
public function work(): void
{
// ....working
}
}
class Robot implements Employee
{
public function work(): void
{
//.... working much more
}
}
class Manager
{
private $employee;
public function __construct(Employee $employee)
{
$this->employee = $employee;
}
public function manage(): void
{
$this->employee->work();
}
}
开发技术
发布于：2021-11-08 14:36
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阅读数：562
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评论：0
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