PHP アロー演算子を解説：簡潔なコード記述法と便利な使い方の紹介

<?php
class Person {
    public $name = 'Taro';
    // 従来の無名関数の記述例
    public function getGreetingClosure() {
        $name = $this->name;
        return function() use ($name) {
            return "Hello, I am " . $name;
        };
    }
    // アロー関数を使った記述例(PHP 7.4以降)
    public function getGreetingArrow() {
        return fn() => "Hello, I am " . $this->name;
    }
}
$person = new Person();
echo $person->name;  // プロパティアクセスの例
echo $person->getGreetingClosure()();
echo $person->getGreetingArrow()();
?>

Taro
Hello, I am Taro
Hello, I am Taro

<?php
class Car {
    public $brand = 'Toyota';
}
// インスタンスの生成
$car = new Car();
// プロパティアクセスによるブランドの取得
echo "Brand: " . $car->brand;  // シンプルなプロパティアクセス
?>

Brand: Toyota

<?php
class Engine {
    public $type = 'V6';
}
class Car {
    public $brand = 'Toyota';
    public $engine;
    public function __construct() {
        $this->engine = new Engine();
    }
}
$car = new Car();
// ネストしたオブジェクト内のプロパティにアクセス
echo "Engine type: " . $car->engine->type;
?>

Engine type: V6

<?php
class Greeter {
    public function sayHello() {
        return "Hello!";
    }
}
$greeter = new Greeter();
// メソッド呼び出しによる挨拶の取得
echo $greeter->sayHello();
?>

Hello!

<?php
class QueryBuilder {
    private $query = "";
    public function select($columns) {
        $this->query .= "SELECT " . $columns . " ";
        return $this;
    }
    public function from($table) {
        $this->query .= "FROM " . $table . " ";
        return $this;
    }
    public function where($condition) {
        $this->query .= "WHERE " . $condition;
        return $this;
    }
    public function getQuery() {
        return $this->query;
    }
}
$queryBuilder = new QueryBuilder();
// 連続メソッドチェーンによるSQLクエリの生成
$query = $queryBuilder->select("*")
                      ->from("users")
                      ->where("id = 1")
                      ->getQuery();
echo $query;
?>

SELECT * FROM users WHERE id = 1

<?php
$numbers = [1, 2, 3, 4];
// アロー関数を使って各要素を自乗
$squaredNumbers = array_map(fn($num) => $num * $num, $numbers);
print_r($squaredNumbers);
?>

Array
(
    [0] => 1
    [1] => 4
    [2] => 9
    [3] => 16
)

<?php
class Formatter {
    private $text;
    public function __construct($text) {
        $this->text = $text;
    }
    public function toUpperCase() {
        $this->text = strtoupper($this->text);
        return $this;
    }
    public function addPrefix($prefix) {
        $this->text = $prefix . $this->text;
        return $this;
    }
    public function getText() {
        return $this->text;
    }
}
// Formatterインスタンスを生成し、連続してメソッドを呼び出す
$result = (new Formatter("hello"))
            ->toUpperCase()
            ->addPrefix("Greeting: ")
            ->getText();
echo $result;
?>

Greeting: HELLO