State を PHP で
State は、 振る舞いに関するデザインパターンの一つで、 オブジェクトの内部状態が変化した時にその振る舞いを変更することを可能とします。
このパターンは、 状態に関連した振る舞いを個別の状態のクラスへ抽出し、 元のオブジェクトが作業を自分で行わず、 これらのクラスのインスタンスに委任することを強制します。
複雑度：
人気度：
使用例： PHP では、 State パターンは、 switch 演算子に基づく巨大で厄介な状態機械をオブジェクトに変換する時に時々使用されます。
見つけ方： オブジェクトが、 その外的に制御される状態によって振る舞いを変えるようなメソッドを持っていたら、 State パターンを識別できます。
概念的な例
この例は、 State デザインパターンの構造を説明するためのものです。 以下の質問に答えることを目的としています：
- どういうクラスからできているか？
- それぞれのクラスの役割は？
- パターンの要素同士はどう関係しているのか？
ここでパターンの構造を学んだ後だと、 これに続く、 現実世界の PHP でのユースケースが理解しやすくなります。
index.php: 概念的な例
<?php
namespace RefactoringGuru\State\Conceptual;
/**
* The Context defines the interface of interest to clients. It also maintains a
* reference to an instance of a State subclass, which represents the current
* state of the Context.
*/
class Context
{
/**
* @var State A reference to the current state of the Context.
*/
private $state;
public function __construct(State $state)
{
$this->transitionTo($state);
}
/**
* The Context allows changing the State object at runtime.
*/
public function transitionTo(State $state): void
{
echo "Context: Transition to " . get_class($state) . ".\n";
$this->state = $state;
$this->state->setContext($this);
}
/**
* The Context delegates part of its behavior to the current State object.
*/
public function request1(): void
{
$this->state->handle1();
}
public function request2(): void
{
$this->state->handle2();
}
}
/**
* The base State class declares methods that all Concrete State should
* implement and also provides a backreference to the Context object, associated
* with the State. This backreference can be used by States to transition the
* Context to another State.
*/
abstract class State
{
/**
* @var Context
*/
protected $context;
public function setContext(Context $context)
{
$this->context = $context;
}
abstract public function handle1(): void;
abstract public function handle2(): void;
}
/**
* Concrete States implement various behaviors, associated with a state of the
* Context.
*/
class ConcreteStateA extends State
{
public function handle1(): void
{
echo "ConcreteStateA handles request1.\n";
echo "ConcreteStateA wants to change the state of the context.\n";
$this->context->transitionTo(new ConcreteStateB());
}
public function handle2(): void
{
echo "ConcreteStateA handles request2.\n";
}
}
class ConcreteStateB extends State
{
public function handle1(): void
{
echo "ConcreteStateB handles request1.\n";
}
public function handle2(): void
{
echo "ConcreteStateB handles request2.\n";
echo "ConcreteStateB wants to change the state of the context.\n";
$this->context->transitionTo(new ConcreteStateA());
}
}
/**
* The client code.
*/
$context = new Context(new ConcreteStateA());
$context->request1();
$context->request2();
Output.txt: 実行結果
Context: Transition to RefactoringGuru\State\Conceptual\ConcreteStateA.
ConcreteStateA handles request1.
ConcreteStateA wants to change the state of the context.
Context: Transition to RefactoringGuru\State\Conceptual\ConcreteStateB.
ConcreteStateB handles request2.
ConcreteStateB wants to change the state of the context.
Context: Transition to RefactoringGuru\State\Conceptual\ConcreteStateA.
現実的な例
この例では、 State パターンを使用して、 請求書のさまざまな状態を表現します。 このアプローチにより、 請求書をある状態から別の状態に移行する際にさまざまな条件チェックを実装でき、 また各状態のロジックを別々のクラスにカプセル化できます。
index.php: 概念的な例
<?php
namespace RefactoringGuru\State\RealWorld;
/**
* State Design Pattern
*
* Intent: lets an object alter its behavior when its internal state changes. It
* appears as if the object changed its class.
*/
/**
* Invoice State Interface
*
* This interface defines the contract that all invoice states must implement.
* It represents the State interface in the State pattern, ensuring that all
* concrete states provide implementations for all possible events/transitions.
*
* The interface defines all possible events that can occur in the invoice
* lifecycle, regardless of whether a particular state can handle them. This
* approach ensures consistency across all states and makes the system more
* maintainable.
*/
interface InvoiceState
{
public function finalize(): void;
public function pay(): void;
public function cancel(): void;
public function void(): void;
public function getName(): string;
}
/**
* Abstract Base State class
*
* This abstract class implements the InvoiceState interface and provides
* default implementations for all state transition methods. The default
* behavior is to throw exceptions for invalid transitions, following the "fail-
* fast" principle.
*
* This approach allows concrete states to only override the methods for
* transitions they actually support, keeping the code clean and focused. Any
* attempt to perform an invalid transition will result in a clear exception
* rather than silent failure.
*
* The abstract class also maintains a reference to the context (Invoice)
* object, which is needed for performing state transitions.
*/
abstract class BaseInvoiceState implements InvoiceState
{
/**
* Reference to the context object (Invoice)
*
* Each state needs access to the context to perform state transitions.
* This creates a bidirectional relationship between the state and context.
*/
protected $invoice;
public function __construct(Invoice $invoice)
{
$this->invoice = $invoice;
}
/**
* Default implementation for finalize event
*
* By default, finalize is not allowed in most states. Only states that
* support this transition will override this method.
*
* @throws InvalidStateTransitionException
*/
public function finalize(): void
{
throw new InvalidStateTransitionException("Cannot finalize invoice in " . $this->getName() . " state");
}
/**
* Default implementation for pay event
*
* By default, payment is not allowed in most states. Only states that
* support this transition will override this method.
*
* @throws InvalidStateTransitionException
*/
public function pay(): void
{
throw new InvalidStateTransitionException("Cannot pay invoice in " . $this->getName() . " state");
}
/**
* Default implementation for cancel event
*
* By default, cancellation is not allowed in most states. Only states that
* support this transition will override this method.
*
* @throws InvalidStateTransitionException
*/
public function cancel(): void
{
throw new InvalidStateTransitionException("Cannot cancel invoice in " . $this->getName() . " state");
}
/**
* Default implementation for void event
*
* By default, voiding is not allowed in most states. Only states that
* support this transition will override this method.
*
* @throws InvalidStateTransitionException
*/
public function void(): void
{
throw new InvalidStateTransitionException("Cannot void invoice in " . $this->getName() . " state");
}
/**
* Abstract method to get the state name
*
* Each concrete state must implement this method to return its name. This
* is used for logging, debugging, and display purposes.
*
* @return string The name of the current state
*/
abstract public function getName(): string;
}
/**
* Each Concrete State corresponds to a specific state.
*
* This Concrete State Represents a draft invoice.
*
* This is the initial state of every invoice. In this state, the invoice is
* still being prepared and can only be finalized to move to the Open state. No
* other operations are allowed in this state.
*/
class DraftInvoiceState extends BaseInvoiceState
{
/**
* Handle finalize event
*
* This is the only valid transition from Draft state. When an invoice is
* finalized, it transitions to the Open state where it can be paid, voided,
* or cancelled.
*/
public function finalize(): void
{
echo "Invoice #{$this->invoice->getId()} finalized - changing from Draft to Open\n";
$this->invoice->setState(new OpenInvoiceState($this->invoice));
}
public function getName(): string
{
return 'draft';
}
}
/**
* This Concrete State Represents an open invoice.
*
* This state represents an invoice that has been finalized and is ready for
* processing. From this state, the invoice can be:
* - Paid (moves to Paid state)
* - Voided (moves to Void state)
* - Cancelled (moves to Uncollectable state)
*/
class OpenInvoiceState extends BaseInvoiceState
{
/**
* Handle pay event
*
* When payment is received, the invoice transitions to the Paid state. This
* is a terminal state - no further operations are allowed.
*/
public function pay(): void
{
echo "Invoice #{$this->invoice->getId()} paid - changing from Open to Paid\n";
$this->invoice->setState(new PaidInvoiceState($this->invoice));
}
/**
* Handle void event
*
* When an invoice is voided, it transitions to the Void state. This is a
* terminal state - no further operations are allowed.
*/
public function void(): void
{
echo "Invoice #{$this->invoice->getId()} voided - changing from Open to Void\n";
$this->invoice->setState(new VoidInvoiceState($this->invoice));
}
/**
* Handle cancel event
*
* When an invoice is cancelled, it transitions to the Uncollectable state.
* From Uncollectable, the invoice can still be paid or voided.
*/
public function cancel(): void
{
echo "Invoice #{$this->invoice->getId()} cancelled - changing from Open to Uncollectable\n";
$this->invoice->setState(new UncollectableInvoiceState($this->invoice));
}
public function getName(): string
{
return 'open';
}
}
/**
* This Concrete State Represents a paid invoice.
*
* This is a terminal state representing a paid invoice. Once an invoice is
* paid, no further state transitions are allowed. All event methods use the
* default implementation which throws exceptions.
*/
class PaidInvoiceState extends BaseInvoiceState
{
public function getName(): string
{
return 'paid';
}
}
/**
* This Concrete State Represents a void invoice.
*
* This is a terminal state representing a voided invoice. Once an invoice is
* voided, no further state transitions are allowed. All event methods use the
* default implementation which throws exceptions.
*/
class VoidInvoiceState extends BaseInvoiceState
{
public function getName(): string
{
return 'void';
}
}
/**
* This Concrete State Represents a collectable invoice.
*
* This state represents an invoice that has been cancelled but can still be
* recovered. From this state, the invoice can be:
* - Paid (moves to Paid state)
* - Voided (moves to Void state)
*
* This provides a way to handle invoices that were cancelled but later can be
* collected or definitively written off.
*/
class UncollectableInvoiceState extends BaseInvoiceState
{
/**
* Handle pay event
*
* Even though the invoice was cancelled, payment can still be received.
* This transitions the invoice to the Paid state.
*/
public function pay(): void
{
echo "Invoice #{$this->invoice->getId()} paid - changing from Uncollectable to Paid\n";
$this->invoice->setState(new PaidInvoiceState($this->invoice));
}
/**
* Handle void event
*
* If the invoice is definitively uncollectable, it can be voided. This
* transitions the invoice to the Void state.
*/
public function void(): void
{
echo "Invoice #{$this->invoice->getId()} voided - changing from Uncollectable to Void\n";
$this->invoice->setState(new VoidInvoiceState($this->invoice));
}
public function getName(): string
{
return 'uncollectable';
}
}
/**
* Context class - Invoice
*
* This is the context class in the State pattern. It maintains a reference to
* the current state object and delegates all state-specific behavior to the
* current state. The context is unaware of the specific state classes and
* interacts with them through the abstract InvoiceState interface.
*
* The context also maintains the invoice's data (id, amount, etc.) that remains
* constant regardless of the state.
*/
class Invoice
{
private $id;
private $amount;
/**
* Current state object
*
* This is the key component of the State pattern. The context maintains a
* reference to the current state object and delegates all state-specific
* operations to this object.
*
* @var InvoiceState
*/
private $state;
private $createdAt;
/**
* Constructor
*
* Creates a new invoice. The invoice always starts in the Draft state as
* per business requirements.
*/
public function __construct(int $id, float $amount)
{
$this->id = $id;
$this->amount = $amount;
$this->createdAt = new \DateTime();
// Initial state is draft This is where the State pattern begins - we
// set the initial state
$this->state = new DraftInvoiceState($this);
}
public function getId(): int
{
return $this->id;
}
/**
* Set the current state
*
* This method is called by state objects to transition to a new state. It's
* the mechanism that allows the State pattern to work - states can change
* the context's state by calling this method.
*
* @param InvoiceState $state The new state object
*/
public function setState(InvoiceState $state)
{
$this->state = $state;
}
/**
* Get the current state object
*
* @return InvoiceState
*/
public function getState(): InvoiceState
{
return $this->state;
}
/**
* Get the current state name
*
* This is a convenience method that delegates to the current state object.
*
* @return string
*/
public function getStateName(): string
{
return $this->state->getName();
}
/**
* Event method: finalize
*
* This method delegates the finalize operation to the current state. This
* is the core of the State pattern - the context doesn't know how to handle
* the operation, so it delegates to the current state.
*/
public function finalize()
{
$this->state->finalize();
}
/**
* Event method: pay
*
* This method delegates the pay operation to the current state. The
* behavior will vary depending on the current state.
*/
public function pay()
{
$this->state->pay();
}
/**
* Event method: cancel
*
* This method delegates the cancel operation to the current state. The
* behavior will vary depending on the current state.
*/
public function cancel()
{
$this->state->cancel();
}
/**
* Event method: void
*
* This method delegates the void operation to the current state. The
* behavior will vary depending on the current state.
*/
public function void()
{
$this->state->void();
}
/**
* Get invoice information
*
* Returns an array with all invoice information including current state.
* This is useful for debugging, logging, or API responses.
*
* @return array
*/
public function getInfo(): array
{
return [
'id' => $this->id,
'amount' => $this->amount,
'state' => $this->getStateName(),
'created_at' => $this->createdAt->format('Y-m-d H:i:s')
];
}
}
/**
* Custom exception for invalid state transitions
*
* This exception is thrown when an invalid state transition is attempted. It
* provides clear error messages about what transition was attempted and why it
* failed.
*/
class InvalidStateTransitionException extends \Exception
{
/**
* Constructor
*
* @param string $message Error message
* @param int $code Error code
* @param \Exception|null $previous Previous exception
*/
public function __construct($message = "", $code = 0, \Exception $previous = null)
{
parent::__construct($message, $code, $previous);
}
}
/**
* ============================================================================
* USAGE EXAMPLE AND DEMONSTRATION
* ============================================================================
*
* The following code demonstrates how to use the State pattern implementation
* with various scenarios that show all possible state transitions.
*/
try {
echo "=== Invoice State Pattern Demo ===\n\n";
// Create a new invoice (starts in draft state)
$invoice = new Invoice(1001, 1500.00);
echo "Created invoice: " . json_encode($invoice->getInfo()) . "\n\n";
// Scenario 1: Draft -> Open -> Paid
echo "--- Scenario 1: Draft -> Open -> Paid ---\n";
$invoice->finalize(); // Draft -> Open
echo "Current state: " . $invoice->getStateName() . "\n";
$invoice->pay(); // Open -> Paid
echo "Current state: " . $invoice->getStateName() . "\n";
// Try to pay again (should fail)
try {
$invoice->pay();
} catch (InvalidStateTransitionException $e) {
echo "Expected error: " . $e->getMessage() . "\n";
}
echo "\n--- Scenario 2: Draft -> Open -> Void ---\n";
$invoice2 = new Invoice(1002, 750.00);
$invoice2->finalize(); // Draft -> Open
$invoice2->void(); // Open -> Void
echo "Invoice 2 state: " . $invoice2->getStateName() . "\n";
echo "\n--- Scenario 3: Draft -> Open -> Uncollectable -> Paid ---\n";
$invoice3 = new Invoice(1003, 2000.00);
$invoice3->finalize(); // Draft -> Open
$invoice3->cancel(); // Open -> Uncollectable
echo "Invoice 3 state: " . $invoice3->getStateName() . "\n";
$invoice3->pay(); // Uncollectable -> Paid
echo "Invoice 3 final state: " . $invoice3->getStateName() . "\n";
echo "\n--- Scenario 4: Draft -> Open -> Uncollectable -> Void ---\n";
$invoice4 = new Invoice(1004, 500.00);
$invoice4->finalize(); // Draft -> Open
$invoice4->cancel(); // Open -> Uncollectable
$invoice4->void(); // Uncollectable -> Void
echo "Invoice 4 final state: " . $invoice4->getStateName() . "\n";
echo "\n--- Error Scenario: Invalid transition ---\n";
$invoice5 = new Invoice(1005, 300.00);
try {
$invoice5->pay(); // Try to pay draft invoice (should fail)
} catch (InvalidStateTransitionException $e) {
echo "Expected error: " . $e->getMessage() . "\n";
}
echo "\n--- State Information ---\n";
echo "Invoice 1: " . json_encode($invoice->getInfo()) . "\n";
echo "Invoice 2: " . json_encode($invoice2->getInfo()) . "\n";
echo "Invoice 3: " . json_encode($invoice3->getInfo()) . "\n";
echo "Invoice 4: " . json_encode($invoice4->getInfo()) . "\n";
echo "Invoice 5: " . json_encode($invoice5->getInfo()) . "\n";
} catch (InvalidStateTransitionException $e) {
echo "Error: " . $e->getMessage() . "\n";
}
Output.txt: 実行結果
=== Invoice State Pattern Demo ===
Created invoice: {"id":1001,"amount":1500,"state":"draft","created_at":"2025-07-12 13:14:15"}
--- Scenario 1: Draft -> Open -> Paid ---
Invoice #1001 finalized - changing from Draft to Open
Current state: open
Invoice #1001 paid - changing from Open to Paid
Current state: paid
Expected error: Cannot pay invoice in paid state
--- Scenario 2: Draft -> Open -> Void ---
Invoice #1002 finalized - changing from Draft to Open
Invoice #1002 voided - changing from Open to Void
Invoice 2 state: void
--- Scenario 3: Draft -> Open -> Uncollectable -> Paid ---
Invoice #1003 finalized - changing from Draft to Open
Invoice #1003 cancelled - changing from Open to Uncollectable
Invoice 3 state: uncollectable
Invoice #1003 paid - changing from Uncollectable to Paid
Invoice 3 final state: paid
--- Scenario 4: Draft -> Open -> Uncollectable -> Void ---
Invoice #1004 finalized - changing from Draft to Open
Invoice #1004 cancelled - changing from Open to Uncollectable
Invoice #1004 voided - changing from Uncollectable to Void
Invoice 4 final state: void
--- Error Scenario: Invalid transition ---
Expected error: Cannot pay invoice in draft state
--- State Information ---
Invoice 1: {"id":1001,"amount":1500,"state":"paid","created_at":"2025-07-12 13:14:15"}
Invoice 2: {"id":1002,"amount":750,"state":"void","created_at":"2025-07-12 13:14:15"}
Invoice 3: {"id":1003,"amount":2000,"state":"paid","created_at":"2025-07-12 13:14:15"}
Invoice 4: {"id":1004,"amount":500,"state":"void","created_at":"2025-07-12 13:14:15"}
Invoice 5: {"id":1005,"amount":300,"state":"draft","created_at":"2025-07-12 13:14:15"}
