PHP中箭头函数的实例详解

//老办法
$this->existingSchemaPaths = array_filter($paths, function ($v) use ($names) {
    return in_array($v, $names);
});

// 使用箭头函数的新方法
$this->existingSchemaPaths = array_filter($paths, fn($v) => in_array($v, $names));

//作用域示例
$discount = 5;
$items = array_map(fn($item) => $item - $discount, $items);

//类型提示
$users = array_map(fn(User $user): int => $user->id, $users);

//展开操作符
function complement(callable $f) {
    return fn(...$args) => !$f(...$args);
}

//嵌套
$z = 1;
$fn = fn($x) => fn($y) => $x * $y + $z;

//有效的函数签名
fn(array $x) => $x;
fn(): int => $x;
fn($x = 42) => $x;
fn(&$x) => $x;
fn&($x) => $x;
fn($x, ...$rest) => $rest;

//现今
class Test {
    public function method() {
        $fn = fn() => var_dump($this);
        $fn(); // object(Test)#1 { ... }

        $fn = static fn() => var_dump($this);
        $fn(); // Error: Using $this when not in object context
    }
}

//也许在未来的某一天
class Test {
    private $foo;
    private $bar;

    fn getFoo() => $this->foo;
    fn getBar() => $this->bar;
}