This article introduces the new features of PHP5.5 ~ PHP7.2. Friends in need can refer to it

Porting from PHP 5.5.x to PHP 5.6.x

New Features

Use expressions to define constants

• In previous versions of PHP, you had to use static values ​​to define constants, declare properties, and specify default values ​​for function parameters. You can now use numeric expressions including numbers, string literals, and other constants to define constants, declare properties, and set default values ​​for function parameters.

You can now define constants of type array through the const keyword. 
Use ... operators to define variable-length parameter functions
Now you can not rely on func_get_args(), Use the ... operator to implement variable-length parameter functions. 
The above routine will output: 
$req: 1; $opt: 0; number of params: 0
$req: 1; $opt: 2; number of params: 0
$req: 1; $opt: 2; number of params: 1
$req: 1; $opt: 2; number of params: 2
Use the ... operator for parameter expansion
 
When calling a function, use the... operator to expand arrays and traversable objects into function parameters. In other programming languages, such as Ruby, this is called the concatenation operator. 
The above routine will output: 
6
use function and use const
use operator has been expanded To support importing external functions and constants into classes. The corresponding structures are use function and use const. 
The above routine will output: 
42
Name\Space\f
Use hash_equals() to compare strings to avoid timing attacks
Ported from PHP 5.6.x to PHP 7.0.x
New features
Scalar type declaration
There are two modes for scalar type declaration: mandatory (default) and strict mode. The following type parameters are now available (either in forced or strict mode): string, int, float, and bool. 
The above routine will output: 
int(9)
Return value type declaration
PHP 7 adds a return type declaration support. Similar to the parameter type declaration, the return type declaration specifies the type of the function's return value. The available types are the same as those available in the parameter declaration. 
null coalescing operator
Since there are a lot of situations where ternary expressions and isset() are used simultaneously in daily use, we add The syntactic sugar of null coalescing operator (??) is added. If the variable exists and is not NULL, it returns its own value, otherwise it returns its second operand. 
Spaceship operator (combined comparison operator)
The spaceship operator is used to compare two expressions. It returns -1, 0 or 1 when $a is less than, equal to or greater than $b respectively. The principle of comparison follows PHP's regular comparison rules. 
 '1'; // 0
echo 1 <=> 2; // -1
echo 2 <=> 1; // 1

// 浮点数
echo '1.50' <=> 1.5; // 0
echo 1.5 <=> 2.5; // -1
echo 2.5 <=> 1.5; // 1
 
// 字符串
echo "a" <=> "a"; // 0
echo "a" <=> "b"; // -1
echo "b" <=> "a"; // 1
?>
Defining constant arrays via define()
Constants of type Array can now be defined via define(). In PHP5.6 it can only be defined via const. 
define('ANIMALS', [
    'dog',
    'cat',
    'bird'
]);

echo ANIMALS[1]; // 输出 "cat"
Closure::call()
Closure::call() now has better performance, short and crisp temporary bindings Closure a method on the object and call it. 
x;};
$getX = $getXCB->bindTo(new A, 'A'); // 中间层闭包
echo $getX();

// PHP 7+ 及更高版本的代码
$getX = function() {return $this->x;};
echo $getX->call(new A);
The above routine will output: 
1
Groupinguse Statement
From the same namespace Imported classes, functions, and constants can now be imported all at once with a single use statement. 
Generators can return expressions
This feature builds on the generator feature introduced in PHP 5.5 version. It allows you to return an expression by using the return syntax in a generator function (but does not allow the return of a reference value). You can get the return value of the generator by calling the Generator::getReturn() method, but this method can only be used when generating Called once after the generator has finished generating work. 
Integer division function intp()

Ported from PHP 7.0.x to PHP 7.1.x
New features
Nullable type
The types of parameters and return values ​​can now be allowed to be null by adding a question mark before the type. When this feature is enabled, the parameters passed in or the result returned by the function are either of the given type or null . 
The above routine will output: 
string(10) "elePHPant"
NULL
string(10) "elePHPant"
NULL
Uncaught Error: Too few arguments to function test(), 0 passed in...
Void function 
A new return value type void is introduced. Methods whose return values ​​are declared of type void either omit the return statement altogether or use an empty return statement. NULL is not a legal return value for void functions. 
The above routine will output: 
null
int(2)
int(1)
Symmetric array destructuring
短数组语法（[]）现在作为list()语法的一个备选项，可以用于将数组的值赋给一些变量（包括在foreach中）。
类常量可见性
现在起支持设置类常量的可见性。
iterable 伪类
现在引入了一个新的被称为iterable的伪类 (与callable类似)。 这可以被用在参数或者返回值类型中，它代表接受数组或者实现了Traversable接口的对象。 至于子类，当用作参数时，子类可以收紧父类的iterable类型到array 或一个实现了Traversable的对象。对于返回值，子类可以拓宽父类的 array或对象返回值类型到iterable。
多异常捕获处理
一个catch语句块现在可以通过管道字符(|)来实现多个异常的捕获。 这对于需要同时处理来自不同类的不同异常时很有用。

list()现在支持键名
现在list()和它的新的[]语法支持在它内部去指定键名。这意味着它可以将任意类型的数组 都赋值给一些变量（与短数组语法类似）
 1, "name" => 'Tom'],
    ["id" => 2, "name" => 'Fred'],
];

// list() style
list("id" => $id1, "name" => $name1) = $data[0];

// [] style
["id" => $id1, "name" => $name1] = $data[0];

// list() style
foreach ($data as list("id" => $id, "name" => $name)) {
    // logic here with $id and $name
}

// [] style
foreach ($data as ["id" => $id, "name" => $name]) {
    // logic here with $id and $name
}

从PHP 7.1.x 移植到 PHP 7.2.x
新特性
新的对象类型
这种新的对象类型, object, 引进了可用于逆变（contravariant）参数输入和协变（covariant）返回任何对象类型。
允许重写抽象方法(Abstract method)
当一个抽象类继承于另外一个抽象类的时候，继承后的抽象类可以重写被继承的抽象类的抽象方法。
abstract class A
{
    abstract function test(string $s);
}
abstract class B extends A
{
    // overridden - still maintaining contravariance for parameters and covariance for return
    abstract function test($s) : int;
}
扩展了参数类型
重写方法和接口实现的参数类型现在可以省略了。不过这仍然是符合LSP，因为现在这种参数类型是逆变的。
interface A
{
    public function Test(array $input);
}

class B implements A
{
    public function Test($input){} // type omitted for $input
}
允许分组命名空间的尾部逗号
命名空间可以在PHP 7中使用尾随逗号进行分组引入。
use Foo\Bar\{
    Foo,
    Bar,
    Baz,
};



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