文章来源refactoringguru.cn/design-patt…
PHP 访问者模式讲解和代码示例
访问者是一种行为设计模式， 允许你在不修改已有代码的情况下向已有类层次结构中增加新的行为。
阅读我们的文章访问者和双分派以了解为什么不能通过方法重载来简单地替换访问者。
复杂度：******
流行度：******
使用示例： 访问者模式在 PHP 代码中不太常用， 因为它不仅复杂， 应用范围也比较狭窄。
真实世界示例
在本例中， 访问者模式在已有类层次结构 （ “公司 > 部门 > 雇员”） 中添加了报表功能
在将访问者构架添加到程序中后， 你就能够在无需修改已有类的前提下将其他类似行为轻松添加到程序中了。
** index.php: 真实世界示例
<?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);
** Output.txt: 执行结果
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)
