Backend Development
PHP7
Teach you to use two lines of code to add a 'non-empty merge' syntactic sugar to PHP7
Teach you to use two lines of code to add a 'non-empty merge' syntactic sugar to PHP7
我们知道从 PHP 5.3 起三元运算符 ? : 有一个写法简洁写法是这样的：
<?php $a = 0; $b = $a ?: 1; # $b === 1
这实际上相当于：
<?php $a = 0; $b = $a ? $a : 1; # $b === 1
在 PHP5 中，语法分析是这样写的：
| expr '?' { zend_do_begin_qm_op(&$1, &$2 TSRMLS_CC); }
expr ':' { zend_do_qm_true(&$4, &$2, &$5 TSRMLS_CC); }
expr { zend_do_qm_false(&$$, &$7, &$2, &$5 TSRMLS_CC); }
| expr '?' ':' { zend_do_jmp_set(&$1, &$2, &$3 TSRMLS_CC); }
expr { zend_do_jmp_set_else(&$$, &$5, &$2, &$3 TSRMLS_CC); }在 PHP7 中，由于 AST（抽象语法树）的引入，语法分析有些简化：
| expr '?' expr ':' expr
{ $$ = zend_ast_create(ZEND_AST_CONDITIONAL, $1, $3, $5); }
| expr '?' ':' expr
{ $$ = zend_ast_create(ZEND_AST_CONDITIONAL, $1, NULL, $4); }PHP7 中语法分析之后都是写到 AST 的节点上。从上面可以看出，简化的 ?: 和完整的三元表达式的区别就是节点中间的值为 NULL。
PHP7 添加了一个合并操作符（T_COALESCE），用于简化 isset 的条件判断：
<?php $b = $a ?? 1;
它相当于：
<?php $b = isset($a) ? $a : 1;
仅仅是 isset 判断，在 为等值时还是会返回b 的值还是为 0 。
这个操作符的语法分析语句是：
| expr T_COALESCE expr
{ $$ = zend_ast_create(ZEND_AST_COALESCE, $1, $3); }如果想将 isset 换成 empty 的效果，也就是说在变量不存在或转换成 boolean 后为 false 都赋予其他值，需要这样写：
<?php $b = $a ?? 1 ?: 1;
显然上面的表达式中中间一部分稍微有些多余，那么做些简化呢？
现在我想添加一个语法 ??: ，它的作用是对变量做 empty 的判断。也就是说达到上面 $a ?? 1 ?: 1 的效果：
<?php $b = $a ??: 1;
改起来很简单，只需要将 ?: 和 ?? 的分析合并一下（注意这里和上面所有的地方 $1 $2 等符号的数字表示的都是变量或者常量出现的位置顺序）：
| expr T_COALESCE ':' expr
{ $$ = zend_ast_create(ZEND_AST_CONDITIONAL,
zend_ast_create(ZEND_AST_COALESCE, $1, $4), NULL, $4); }仅仅只有两句，因为并没有在词法分析器中添加 Token，所以只能算是个语法糖。
重新编译一下之后就能看到效果啦。
测试：
$ /usr/local/php/bin/php -r "\$a = 0; echo \$a ?? 1, PHP_EOL;" 0 $ /usr/local/php/bin/php -r "\$a = 0; echo \$a ??: 1, PHP_EOL;" 1
The above is the detailed content of Teach you to use two lines of code to add a 'non-empty merge' syntactic sugar to PHP7. For more information, please follow other related articles on the PHP Chinese website!
Hot AI Tools
Undress AI Tool
Undress images for free
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Clothoff.io
AI clothes remover
Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!
Hot Article
Hot Tools
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
What should I do if the plug-in is installed in php7.0 but it still shows that it is not installed?
Apr 02, 2024 pm 07:39 PM
To resolve the plugin not showing installed issue in PHP 7.0: Check the plugin configuration and enable the plugin. Restart PHP to apply configuration changes. Check the plugin file permissions to make sure they are correct. Install missing dependencies to ensure the plugin functions properly. If all other steps fail, rebuild PHP. Other possible causes include incompatible plugin versions, loading the wrong version, or PHP configuration issues.
How to solve the problem when php7 detects that the tcp port is not working
Mar 22, 2023 am 09:30 AM
In php5, we can use the fsockopen() function to detect the TCP port. This function can be used to open a network connection and perform some network communication. But in php7, the fsockopen() function may encounter some problems, such as being unable to open the port, unable to connect to the server, etc. In order to solve this problem, we can use the socket_create() function and socket_connect() function to detect the TCP port.
Why does an error occur when installing an extension using PECL in a Docker environment? How to solve it?
Apr 01, 2025 pm 03:06 PM
Causes and solutions for errors when using PECL to install extensions in Docker environment When using Docker environment, we often encounter some headaches...
How to install mongo extension in php7.0
Nov 21, 2022 am 10:25 AM
How to install the mongo extension in php7.0: 1. Create the mongodb user group and user; 2. Download the mongodb source code package and place the source code package in the "/usr/local/src/" directory; 3. Enter "src/" directory; 4. Unzip the source code package; 5. Create the mongodb file directory; 6. Copy the files to the "mongodb/" directory; 7. Create the mongodb configuration file and modify the configuration.
PHP Server Environment FAQ Guide: Quickly Solve Common Problems
Apr 09, 2024 pm 01:33 PM
Common solutions for PHP server environments include ensuring that the correct PHP version is installed and that relevant files have been copied to the module directory. Disable SELinux temporarily or permanently. Check and configure PHP.ini to ensure that necessary extensions have been added and set up correctly. Start or restart the PHP-FPM service. Check the DNS settings for resolution issues.
How to automatically set permissions of unixsocket after system restart?
Mar 31, 2025 pm 11:54 PM
How to automatically set the permissions of unixsocket after the system restarts. Every time the system restarts, we need to execute the following command to modify the permissions of unixsocket: sudo...
How to install and deploy php7.0
Nov 30, 2022 am 09:56 AM
How to install and deploy php7.0: 1. Go to the PHP official website to download the installation version corresponding to the local system; 2. Extract the downloaded zip file to the specified directory; 3. Open the command line window and go to the "E:\php7" directory Just run the "php -v" command.
Record once and use strace to diagnose the problem of PHP occupying too much system resources.
May 03, 2024 pm 04:31 PM
Local environment: redhat6.7 system. nginx1.12.1, php7.1.0, the code uses the yii2 framework problem: the local web site needs to use the elasticsearch service. When PHP uses elasticsearch built on a local server, the local load is normal. When I use AWS's elasticsearch service, the load on the local server is often too high. Check the nginx and php logs and find no exceptions. The number of concurrent connections in the system is also not high. At this time, I thought of a strace diagnostic tool that our boss told me. Debugging process: Find a php sub-process idstrace-
