<?php
function answer(): ?int {
 return null; //ok
}

function answer(): ?int {
 return 42; // ok
}

function say(?string $msg) {
 if ($msg) {
 echo $msg;
 }
}

<?php
interface Fooable {
 function foo(?Fooable $f);
}

<?php
function foo_nullable(?Bar $bar) {}

foo_nullable(new Bar); // 可行
foo_nullable(null); // 可行
foo_nullable(); // 不可行

<?php
// 5.4 之前
$array = array(1, 2, 3);
$array = array("a" => 1, "b" => 2, "c" => 3);

// 5.4 及之后
$array = [1, 2, 3];
$array = ["a" => 1, "b" => 2, "c" => 3];

<?php
list($a, $b, $c) = $array;

<?php
[$a, $b, $c] = $array;

<?php
["a" => $a, "b" => $b, "c" => $c] = $array;

<?php
foreach ($points as ["x" => $x, "y" => $y]) {
 var_dump($x, $y);
}

<?php
// 不合法
list([$a, $b], [$c, $d]) = [[1, 2], [3, 4]];

// 不合法
[list($a, $b), list($c, $d)] = [[1, 2], [3, 4]];

// 合法
[[$a, $b], [$c, $d]] = [[1, 2], [3, 4]];

<?php
$array = ["a" => 1, "b" => 2, "c" => 3];
["a" => $a, "b" => $b, "c" => $c] = $array;

<?php
$a = $array['a'];
$b = $array['b'];
$c = $array['c'];

<?php
list($a, $b) = [1 => '1', 2 => '2'];

<?php
list(1 => $a, 2 => $b) = [1 => '1', 2 => '2'];

<?php
// Parse error: syntax error, ...
list($unkeyed, "key" => $keyed) = $array;

<?php
$points = [
 ["x" => 1, "y" => 2],
 ["x" => 2, "y" => 1]
];

list(list("x" => $x1, "y" => $y1), list("x" => $x2, "y" => $y2)) = $points;

$points = [
 "first" => [1, 2],
 "second" => [2, 1]
];

list("first" => list($x1, $y1), "second" => list($x2, $y2)) = $points;

<?php
$points = [
 ["x" => 1, "y" => 2],
 ["x" => 2, "y" => 1]
];

foreach ($points as list("x" => $x, "y" => $y)) {
 echo "Point at ($x, $y)", PHP_EOL;
}

<?php
function should_return_nothing(): void {
 return 1; // Fatal error: A void function must not return a value
}

<?php
function lacks_return(): void {
 // valid
}

function returns_nothing(): void {
 return; // valid
}

<?php
function returns_one(): void {
 return 1; // Fatal error: A void function must not return a value
}

function returns_null(): void {
 return null; // Fatal error: A void function must not return a value
}

<?php
function foobar(void $foo) { // Fatal error: void cannot be used as a parameter type
}

<?php
class Foo
{
 public function bar(): void {
 }
}

class Foobar extends Foo
{
 public function bar(): array { // Fatal error: Declaration of Foobar::bar() must be compatible with Foo::bar(): void
 }
}

<?php
class Token {
 // 常量默认为 public
 const PUBLIC_CONST = 0;

 // 可以自定义常量的可见范围
 private const PRIVATE_CONST = 0;
 protected const PROTECTED_CONST = 0;
 public const PUBLIC_CONST_TWO = 0;

 // 多个常量同时声明只能有一个属性
 private const FOO = 1, BAR = 2;
}

<?php
interface ICache {
 public const PUBLIC = 0;
 const IMPLICIT_PUBLIC = 1;
}

<?php
class testClass {
 const TEST_CONST = 'test';
}

$obj = new ReflectionClass( "testClass" );
$const = $obj->getReflectionConstant( "TEST_CONST" );
$consts = $obj->getReflectionConstants();

<?php
try {
 // Some code...
} catch (ExceptionType1 $e) {
 // 处理 ExceptionType1
} catch (ExceptionType2 $e) {
 // 处理 ExceptionType2
} catch (\Exception $e) {
 // ...
}

<?php
try {
 // Some code...
} catch (ExceptionType1 | ExceptionType2 $e) {
 // 对于 ExceptionType1 和 ExceptionType2 的处理
} catch (\Exception $e) {
 // ...
}