两行代码给 PHP7 添加一个“非空合并”语法糖
我们知道从 PHP 5.3 起三元运算符 ? : 在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 $a 为 0 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
Enjoy IT!
私博地址:http://0x1.im

Hot AI Tools

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Undress AI Tool
Undress images for free

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)

Hot Topics

JWT is an open standard based on JSON, used to securely transmit information between parties, mainly for identity authentication and information exchange. 1. JWT consists of three parts: Header, Payload and Signature. 2. The working principle of JWT includes three steps: generating JWT, verifying JWT and parsing Payload. 3. When using JWT for authentication in PHP, JWT can be generated and verified, and user role and permission information can be included in advanced usage. 4. Common errors include signature verification failure, token expiration, and payload oversized. Debugging skills include using debugging tools and logging. 5. Performance optimization and best practices include using appropriate signature algorithms, setting validity periods reasonably,

The enumeration function in PHP8.1 enhances the clarity and type safety of the code by defining named constants. 1) Enumerations can be integers, strings or objects, improving code readability and type safety. 2) Enumeration is based on class and supports object-oriented features such as traversal and reflection. 3) Enumeration can be used for comparison and assignment to ensure type safety. 4) Enumeration supports adding methods to implement complex logic. 5) Strict type checking and error handling can avoid common errors. 6) Enumeration reduces magic value and improves maintainability, but pay attention to performance optimization.

Session hijacking can be achieved through the following steps: 1. Obtain the session ID, 2. Use the session ID, 3. Keep the session active. The methods to prevent session hijacking in PHP include: 1. Use the session_regenerate_id() function to regenerate the session ID, 2. Store session data through the database, 3. Ensure that all session data is transmitted through HTTPS.

The application of SOLID principle in PHP development includes: 1. Single responsibility principle (SRP): Each class is responsible for only one function. 2. Open and close principle (OCP): Changes are achieved through extension rather than modification. 3. Lisch's Substitution Principle (LSP): Subclasses can replace base classes without affecting program accuracy. 4. Interface isolation principle (ISP): Use fine-grained interfaces to avoid dependencies and unused methods. 5. Dependency inversion principle (DIP): High and low-level modules rely on abstraction and are implemented through dependency injection.

Static binding (static::) implements late static binding (LSB) in PHP, allowing calling classes to be referenced in static contexts rather than defining classes. 1) The parsing process is performed at runtime, 2) Look up the call class in the inheritance relationship, 3) It may bring performance overhead.

RESTAPI design principles include resource definition, URI design, HTTP method usage, status code usage, version control, and HATEOAS. 1. Resources should be represented by nouns and maintained at a hierarchy. 2. HTTP methods should conform to their semantics, such as GET is used to obtain resources. 3. The status code should be used correctly, such as 404 means that the resource does not exist. 4. Version control can be implemented through URI or header. 5. HATEOAS boots client operations through links in response.

In PHP, exception handling is achieved through the try, catch, finally, and throw keywords. 1) The try block surrounds the code that may throw exceptions; 2) The catch block handles exceptions; 3) Finally block ensures that the code is always executed; 4) throw is used to manually throw exceptions. These mechanisms help improve the robustness and maintainability of your code.

The main function of anonymous classes in PHP is to create one-time objects. 1. Anonymous classes allow classes without names to be directly defined in the code, which is suitable for temporary requirements. 2. They can inherit classes or implement interfaces to increase flexibility. 3. Pay attention to performance and code readability when using it, and avoid repeatedly defining the same anonymous classes.
