Interpreter Pattern
言語の文法
<Job> ::= begin <CommandList> <CommandList> ::= <Command>* end <Command> ::= diskspace | date | line
interface Command {
public function execute(Context $context);
}
JobCommand.php
<Job> ::= begin <CommandList>
class JobCommand implements Command {
public function execute(Context $context) {
if($context->getCurrentCommand() !== 'begin') {
throw new RuntimeException();
}
$commandList = new CommandListCommand();
$commandList->execute($context->next);
}
}
CommandListCommand.php
<CommandList> ::= <Command>* end
class CommandListCommand implements Command {
public function execute(Context $context) {
while(true) {
$currentCommand = $context->getCurrentCommand();
if(is_null($currentCommand)) {
throw new RuntimeException();
}
else if($currentCommand === 'end') {
break;
}
else {
$command = new CommandCommand();
$command->execute($context);
}
}
$context->next();
}
}
CommandCommand.php
<Command> ::= diskspace | date | line
class CommandCommand implements Command {
public function execute(Context $context) {
$currentCommand = $context->getCurrentCommand();
if($currentCommand === 'diskspace') {
// 空き容量を計算して出力
}
else if($currentCommand === 'date') {
// 日付出力
}
else if($currentCommand === 'line') {
// 罫線を出力
}
else {
new RuntimeException();
}
}
}
Context.php
class Context {
private $commands;
private $currentIndex = 0;
private $maxIndex = 0;
public function __construct($command) {
$this->commands = split(' +', trim($command));
$this->maxIndex = count($this->commands);
}
public function next() {
$this->currentIndex++;
return $this;
}
public function getCurrentCommand() {
if(!array_key_exists($this->currentIndex, $this->commands)) {
return null;
}
return trim($this->commands[$this->currentIndex]);
}
}
■クライアントコード
$job = new JobCommand();
$job->execute(new Context('begin date line diskspace end'));
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