Detailed explanation of new features in PHP7.1 and 7.2

I have previously introduced to you the detailed explanation of the new features of php7.0. Today, let’s take a look at the new features of php7.1 and php7.2. Function.

php7.1 New features

1. Nullable type

Parameters and return values A type declaration can be marked null by adding a question mark (?) before the type name. Indicates that the type of the function parameter or return value is either the specified type or null.

Look at the example:

function testReturn(?string $name)
{
    return $name;
}
var_dump(testReturn('yangyi'));
var_dump(testReturn(null));
var_dump(testReturn2());

Print output:

$ php php71.php
string(6) "yangyi"
NULL
PHP Fatal error:  Uncaught ArgumentCountError: Too few arguments to function testReturn(), 0 passed in php71.php on line 22 and exactly 1 expected in php71.php:14
Stack trace:
#0 php71.php(22): testReturn()
#1 {main}
  thrown in php71.php on line 14

Same as above: The third one reported a fatal error.

Let’s look at the situation where the function return value is Nullable:

function testReturn3() : ?string
{
    //return "abc";
    //return null;
}
var_dump(testReturn3());

If added? Either return string or null. You cannot return nothing. An error will be reported.

2.void return type

PHP7.0 added the feature of specifying function return type, but the return type cannot be specified as void. This feature of 7.1 is considered a Replenish. A function defined with a return type of void cannot have a return value, even if it returns null:

function testReturn4() : void
{
    //1. 要么啥都不返还 ok
    //2. 要么只return; ok
    //return;
    //3. return null 也会报错
    //return null;
    //4. return 4 会报错
    //return 4;
}
Fatal error: A void function must not return a value in /php71.php on line 70

Also, void can only be used for return values ​​and not for parameters. For example, the following error will be reported:

function testReturn6(void $a) : void
{
}
var_dump(testReturn6());
PHP Fatal error:  void cannot be used as a parameter type in php71.php on line 73

If a method is declared as a void return type in the inheritance of a class, if the subclass inherits and overrides it, it can only return void, otherwise an error will be triggered:

<?php 
class Foo
{
    public function bar(): void {
    }
}
class Foobar extends Foo
{
    // 覆盖失败
    public function bar(): array { 
        // Fatal error: Declaration of Foobar::bar() must be compatible with Foo::bar(): void
    }
}

So, you must do this, so you won’t report an error:

class Foo
{
    public $a;
    public function bar(): void {
        $this->a = 2;
    }
}
class Foobar extends Foo
{
    // 覆盖成功
    public function bar(): void {
        $this->a = 3;
    }
}

3.list’s square brackets ([]) abbreviation and adding the specified key

can be used list to quickly traverse to get the values ​​in the array. The abbreviation [] can now be used.

$data = [
    [1, 'Tom'],
    [2, 'Fred'],
];
// list() style
list($id1, $name1) = $data[0];
// [] style
[$id1, $name1] = $data[0];
// list() style
foreach ($data as list($id, $name)) {
    // logic here with $id and $name
}
// [] style
foreach ($data as [$id, $name]) {
    // logic here with $id and $name
}

In addition, this updated list can also specify a key for the index array. This upgrade is great and very convenient.

$data = [
    ["id" => 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
}

Before this function was not available, we usually used the while each method to traverse the index array using list:

$data = [
    ["id" => 1, "name" => 'Tom'],
    ["id" => 2, "name" => 'Fred'],
];
while (list($id, name) = each($data)) {
    echo "$key => $val\n";
}

Note: The each function has been removed in PHP 7.2! Therefore, don’t use this method to traverse the index array

4. Setting the visible range of class constants

Before, the constants in the class were declared as const, but there was no Visible properties. Now the visible attributes of the method are transplanted:

<?php 
class ConstDemo 
{
    // 常量默认为 public
    const PUBLIC_CONST = 0;
    // 可以自定义常量的可见范围
    public const PUBLIC_CONST_B = 2;
    protected const PROTECTED_CONST = 3;
    private const PRIVATE_CONST = 4;
    // 多个常量同时声明只能有一个属性
    private const FOO = 1, BAR = 2;
}

The usage method is the same as the class method. No more details.

5. Support negative string offset

There are 2 updates, 1 is to take the string directly, 2 is that the third parameter of strpos function supports negative numbers. Indicates taking from the tail.

var_dump("abcdef"[-2]); // e
var_dump(strpos("aabbcc", "b", -3)); //3

The string variable can take the value directly without passing the variable name. It was added in php5.5. Now you can take it from the tail:

var_dump("abcdef"[-2]); // 从末尾取倒数第2个字符：e
var_dump("abcdef"[2]); // 从前面取第2个，从0开始：c
$string = 'bar';
echo $string[1], $string[-1]; // a r

6. Multi-condition catch

In the previous try...catch statement, only one condition can be set for each catch Judgment:

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

can now be processed together. Separate with "|".

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

php7.2

php 7.2 is mostly a bottom-level update to improve performance. There are not many updates at the common syntax level, so we will skip them here.

Related recommendations: "PHP Tutorial"

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