简述PHP7.4 新特性和废弃的功能

<?php
class User {
 public int $age;
 public string $name
} 
$user = new User();
$user->age = 10;
$user->name = "张三";
//error
$user->age = "zhang";//需要传递int

<?php
$factor = 10;
$nums = array_map(fn($n)=>$n * $factor,[1,2,3]);//[10,20,30]
//之前的写法
$nums = array_map(function($num)use($factor){
 return $num * $factor;
},[1,2,3])

<?php
class A {}
class B extends A {}

class Producer {
  public function method(): A {}
}
class ChildProducer extends Producer {
  public function method(): B {}
}
?>

<?php
$parts = ['apple', 'pear'];
$fruits = ['banana', 'orange', ...$parts, 'watermelon'];//['banana', 'orange', 'apple', 'pear', 'watermelon'];
//老的写法
$fruits = array_merge(['banana', 'orange'],$parts,['watermelon']);

<?php
$array['key'] ??= computeDefault();
// 老的写法
if (!isset($array['key'])) {
  $array['key'] = computeDefault();
}
?>

<?php
6.674_083e-11; // float
299_792_458;  // decimal
0xCAFE_F00D;  // hexadecimal
0b0101_1111;  // binary
?>

<?php
 filter_var(1.00,FILTER_VALIDATE_FLOAT);

<?php
 strip_tags($str,['p','a','div']);
//老的写法
strip_tags($str,"<p><a><div>");

<?php
1 ? 2 : 3 ? 4 : 5;  // deprecated
(1 ? 2 : 3) ? 4 : 5; // ok
1 ? 2 : (3 ? 4 : 5); // ok
?>

<?php
$arr = ["a"=>"111"];
$index = "a";
$arr{$index}//废弃
$arr[$index];

<?php
 $num = "";
 $a = (real) $num;//废弃
$a = (float) $num;

<?php
 class Test{
 public function index() 
 {
  return parent::index();//编译错误
 }
}