Template Method em PHP
O Template Method é um padrão de projeto comportamental que permite definir o esqueleto de um algoritmo em uma classe base e permitir que as subclasses substituam as etapas sem alterar a estrutura geral do algoritmo.
Complexidade:
Popularidade:
Exemplos de uso: O padrão Template Method é bastante comum nos frameworks PHP. O padrão simplifica a extensão do comportamento de uma estrutura padrão usando a herança de classe.
Identificação: O Template Method pode ser reconhecido por métodos comportamentais que já possuem um comportamento “padrão” definido pela classe base.
Exemplo conceitual
Este exemplo ilustra a estrutura do padrão de projeto Template Method. Ele se concentra em responder a estas perguntas:
- De quais classes ele consiste?
- Quais papéis essas classes desempenham?
- De que maneira os elementos do padrão estão relacionados?
Depois de aprender sobre a estrutura do padrão, será mais fácil entender o exemplo a seguir, com base em um caso de uso PHP do mundo real.
index.php: Exemplo conceitual
<?php
namespace RefactoringGuru\TemplateMethod\Conceptual;
/**
* The Abstract Class defines a template method that contains a skeleton of some
* algorithm, composed of calls to (usually) abstract primitive operations.
*
* Concrete subclasses should implement these operations, but leave the template
* method itself intact.
*/
abstract class AbstractClass
{
/**
* The template method defines the skeleton of an algorithm.
*/
final public function templateMethod(): void
{
$this->baseOperation1();
$this->requiredOperations1();
$this->baseOperation2();
$this->hook1();
$this->requiredOperation2();
$this->baseOperation3();
$this->hook2();
}
/**
* These operations already have implementations.
*/
protected function baseOperation1(): void
{
echo "AbstractClass says: I am doing the bulk of the work\n";
}
protected function baseOperation2(): void
{
echo "AbstractClass says: But I let subclasses override some operations\n";
}
protected function baseOperation3(): void
{
echo "AbstractClass says: But I am doing the bulk of the work anyway\n";
}
/**
* These operations have to be implemented in subclasses.
*/
abstract protected function requiredOperations1(): void;
abstract protected function requiredOperation2(): void;
/**
* These are "hooks." Subclasses may override them, but it's not mandatory
* since the hooks already have default (but empty) implementation. Hooks
* provide additional extension points in some crucial places of the
* algorithm.
*/
protected function hook1(): void
{
}
protected function hook2(): void
{
}
}
/**
* Concrete classes have to implement all abstract operations of the base class.
* They can also override some operations with a default implementation.
*/
class ConcreteClass1 extends AbstractClass
{
protected function requiredOperations1(): void
{
echo "ConcreteClass1 says: Implemented Operation1\n";
}
protected function requiredOperation2(): void
{
echo "ConcreteClass1 says: Implemented Operation2\n";
}
}
/**
* Usually, concrete classes override only a fraction of base class' operations.
*/
class ConcreteClass2 extends AbstractClass
{
protected function requiredOperations1(): void
{
echo "ConcreteClass2 says: Implemented Operation1\n";
}
protected function requiredOperation2(): void
{
echo "ConcreteClass2 says: Implemented Operation2\n";
}
protected function hook1(): void
{
echo "ConcreteClass2 says: Overridden Hook1\n";
}
}
/**
* The client code calls the template method to execute the algorithm. Client
* code does not have to know the concrete class of an object it works with, as
* long as it works with objects through the interface of their base class.
*/
function clientCode(AbstractClass $class)
{
// ...
$class->templateMethod();
// ...
}
echo "Same client code can work with different subclasses:\n";
clientCode(new ConcreteClass1());
echo "\n";
echo "Same client code can work with different subclasses:\n";
clientCode(new ConcreteClass2());
Output.txt: Resultados da execução
Same client code can work with different subclasses:
AbstractClass says: I am doing bulk of the work
ConcreteClass1 says: Implemented Operation1
AbstractClass says: But I let subclasses to override some operations
ConcreteClass1 says: Implemented Operation2
AbstractClass says: But I am doing bulk of the work anyway
Same client code can work with different subclasses:
AbstractClass says: I am doing bulk of the work
ConcreteClass2 says: Implemented Operation1
AbstractClass says: But I let subclasses to override some operations
ConcreteClass2 says: Overridden Hook1
ConcreteClass2 says: Implemented Operation2
AbstractClass says: But I am doing bulk of the work anyway
Exemplo do mundo real
Neste exemplo, o padrão Template Method define um esqueleto do algoritmo de postagem de mensagens nas redes sociais. Cada subclasse representa uma rede social separada e implementa todas as etapas de maneira diferente, mas reutiliza o algoritmo base.
index.php: Exemplo do mundo real
<?php
namespace RefactoringGuru\TemplateMethod\RealWorld;
/**
* The Abstract Class defines the template method and declares all its steps.
*/
abstract class SocialNetwork
{
protected $username;
protected $password;
public function __construct(string $username, string $password)
{
$this->username = $username;
$this->password = $password;
}
/**
* The actual template method calls abstract steps in a specific order. A
* subclass may implement all of the steps, allowing this method to actually
* post something to a social network.
*/
public function post(string $message): bool
{
// Authenticate before posting. Every network uses a different
// authentication method.
if ($this->logIn($this->username, $this->password)) {
// Send the post data. All networks have different APIs.
$result = $this->sendData($message);
// ...
$this->logOut();
return $result;
}
return false;
}
/**
* The steps are declared abstract to force the subclasses to implement them
* all.
*/
abstract public function logIn(string $userName, string $password): bool;
abstract public function sendData(string $message): bool;
abstract public function logOut(): void;
}
/**
* This Concrete Class implements the Facebook API (all right, it pretends to).
*/
class Facebook extends SocialNetwork
{
public function logIn(string $userName, string $password): bool
{
echo "\nChecking user's credentials...\n";
echo "Name: " . $this->username . "\n";
echo "Password: " . str_repeat("*", strlen($this->password)) . "\n";
simulateNetworkLatency();
echo "\n\nFacebook: '" . $this->username . "' has logged in successfully.\n";
return true;
}
public function sendData(string $message): bool
{
echo "Facebook: '" . $this->username . "' has posted '" . $message . "'.\n";
return true;
}
public function logOut(): void
{
echo "Facebook: '" . $this->username . "' has been logged out.\n";
}
}
/**
* This Concrete Class implements the Twitter API.
*/
class Twitter extends SocialNetwork
{
public function logIn(string $userName, string $password): bool
{
echo "\nChecking user's credentials...\n";
echo "Name: " . $this->username . "\n";
echo "Password: " . str_repeat("*", strlen($this->password)) . "\n";
simulateNetworkLatency();
echo "\n\nTwitter: '" . $this->username . "' has logged in successfully.\n";
return true;
}
public function sendData(string $message): bool
{
echo "Twitter: '" . $this->username . "' has posted '" . $message . "'.\n";
return true;
}
public function logOut(): void
{
echo "Twitter: '" . $this->username . "' has been logged out.\n";
}
}
/**
* A little helper function that makes waiting times feel real.
*/
function simulateNetworkLatency()
{
$i = 0;
while ($i < 5) {
echo ".";
sleep(1);
$i++;
}
}
/**
* The client code.
*/
echo "Username: \n";
$username = readline();
echo "Password: \n";
$password = readline();
echo "Message: \n";
$message = readline();
echo "\nChoose the social network to post the message:\n" .
"1 - Facebook\n" .
"2 - Twitter\n";
$choice = readline();
// Now, let's create a proper social network object and send the message.
if ($choice == 1) {
$network = new Facebook($username, $password);
} elseif ($choice == 2) {
$network = new Twitter($username, $password);
} else {
die("Sorry, I'm not sure what you mean by that.\n");
}
$network->post($message);
Output.txt: Resultados da execução
Username:
> neo
Password:
> 123123
Message:
> What is the Matrix?
Choose the social network to post the message:
1 - Facebook
2 - Twitter
> 1
Checking user's credentials...
Name: neo
Password: ******
.....
Facebook: 'neo' has logged in successfully.
Facebook: 'neo' has posted 'What is the Matrix?'.
Facebook: 'neo' has been logged out.
