PHP 访问者模式讲解和代码示例

<?php

namespace RefactoringGuru\Visitor\RealWorld;

/**
 * The Component interface declares a method of accepting visitor objects.
 *
 * In this method, a Concrete Component must call a specific Visitor's method
 * that has the same parameter type as that component.
 */
interface Entity
{
    public function accept(Visitor $visitor): string;
}

/**
 * The Company Concrete Component.
 */
class Company implements Entity
{
    private $name;

    /**
     * @var Department[]
     */
    private $departments;

    public function __construct(string $name, array $departments)
    {
        $this->name = $name;
        $this->departments = $departments;
    }

    public function getName(): string
    {
        return $this->name;
    }

    public function getDepartments(): array
    {
        return $this->departments;
    }

    // ...

    public function accept(Visitor $visitor): string
    {
        // See, the Company component must call the visitCompany method. The
        // same principle applies to all components.
        return $visitor->visitCompany($this);
    }
}

/**
 * The Department Concrete Component.
 */
class Department implements Entity
{
    private $name;

    /**
     * @var Employee[]
     */
    private $employees;

    public function __construct(string $name, array $employees)
    {
        $this->name = $name;
        $this->employees = $employees;
    }

    public function getName(): string
    {
        return $this->name;
    }

    public function getEmployees(): array
    {
        return $this->employees;
    }

    public function getCost(): int
    {
        $cost = 0;
        foreach ($this->employees as $employee) {
            $cost += $employee->getSalary();
        }

        return $cost;
    }

    // ...

    public function accept(Visitor $visitor): string
    {
        return $visitor->visitDepartment($this);
    }
}

/**
 * The Employee Concrete Component.
 */
class Employee implements Entity
{
    private $name;

    private $position;

    private $salary;

    public function __construct(string $name, string $position, int $salary)
    {
        $this->name = $name;
        $this->position = $position;
        $this->salary = $salary;
    }

    public function getName(): string
    {
        return $this->name;
    }

    public function getPosition(): string
    {
        return $this->position;
    }

    public function getSalary(): int
    {
        return $this->salary;
    }

    // ...

    public function accept(Visitor $visitor): string
    {
        return $visitor->visitEmployee($this);
    }
}

/**
 * The Visitor interface declares a set of visiting methods for each of the
 * Concrete Component classes.
 */
interface Visitor
{
    public function visitCompany(Company $company): string;

    public function visitDepartment(Department $department): string;

    public function visitEmployee(Employee $employee): string;
}

/**
 * The Concrete Visitor must provide implementations for every single class of
 * the Concrete Components.
 */
class SalaryReport implements Visitor
{
    public function visitCompany(Company $company): string
    {
        $output = "";
        $total = 0;

        foreach ($company->getDepartments() as $department) {
            $total += $department->getCost();
            $output .= "\n--" . $this->visitDepartment($department);
        }

        $output = $company->getName() .
            " (" . money_format("%i", $total) . ")\n" . $output;

        return $output;
    }

    public function visitDepartment(Department $department): string
    {
        $output = "";

        foreach ($department->getEmployees() as $employee) {
            $output .= "   " . $this->visitEmployee($employee);
        }

        $output = $department->getName() .
            " (" . money_format("%i", $department->getCost()) . ")\n\n" .
            $output;

        return $output;
    }

    public function visitEmployee(Employee $employee): string
    {
        return money_format("%#6n", $employee->getSalary()) .
            " " . $employee->getName() .
            " (" . $employee->getPosition() . ")\n";
    }
}

/**
 * The client code.
 */

$mobileDev = new Department("Mobile Development", [
    new Employee("Albert Falmore", "designer", 100000),
    new Employee("Ali Halabay", "programmer", 100000),
    new Employee("Sarah Konor", "programmer", 90000),
    new Employee("Monica Ronaldino", "QA engineer", 31000),
    new Employee("James Smith", "QA engineer", 30000),
]);
$techSupport = new Department("Tech Support", [
    new Employee("Larry Ulbrecht", "supervisor", 70000),
    new Employee("Elton Pale", "operator", 30000),
    new Employee("Rajeet Kumar", "operator", 30000),
    new Employee("John Burnovsky", "operator", 34000),
    new Employee("Sergey Korolev", "operator", 35000),
]);
$company = new Company("SuperStarDevelopment", [$mobileDev, $techSupport]);

setlocale(LC_MONETARY, 'en_US');
$report = new SalaryReport();

echo "Client: I can print a report for a whole company:\n\n";
echo $company->accept($report);

echo "\nClient: ...or for different entities " .
    "such as an employee, a department, or the whole company:\n\n";
$someEmployee = new Employee("Some employee", "operator", 35000);
$differentEntities = [$someEmployee, $techSupport, $company];
foreach ($differentEntities as $entity) {
    echo $entity->accept($report) . "\r\n";
}

// $export = new JSONExport(); 
// echo $company->accept($export);

Client: I can print a report for a whole company:

SuperStarDevelopment (USD550,000.00)

--Mobile Development (USD351,000.00)

    $100,000.00 Albert Falmore (designer)
    $100,000.00 Ali Halabay (programmer)
    $ 90,000.00 Sarah Konor (programmer)
    $ 31,000.00 Monica Ronaldino (QA engineer)
    $ 30,000.00 James Smith (QA engineer)

--Tech Support (USD199,000.00)

    $ 70,000.00 Larry Ulbrecht (supervisor)
    $ 30,000.00 Elton Pale (operator)
    $ 30,000.00 Rajeet Kumar (operator)
    $ 34,000.00 John Burnovsky (operator)
    $ 35,000.00 Sergey Korolev (operator)


Client: ...or for different entities such as an employee, a department, or the whole company:

35000 Some employee (operator)

Tech Support (199000)

   70000 Larry Ulbrecht (supervisor)
   30000 Elton Pale (operator)
   30000 Rajeet Kumar (operator)
   34000 John Burnovsky (operator)
   35000 Sergey Korolev (operator)

SuperStarDevelopment (550000)

--Mobile Development (351000)

   100000 Albert Falmore (designer)
   100000 Ali Halabay (programmer)
   90000 Sarah Konor (programmer)
   31000 Monica Ronaldino (QA engineer)
   30000 James Smith (QA engineer)

--Tech Support (199000)

   70000 Larry Ulbrecht (supervisor)
   30000 Elton Pale (operator)
   30000 Rajeet Kumar (operator)
   34000 John Burnovsky (operator)
   35000 Sergey Korolev (operator)