Discuss the syntax differences between PHP7 and PHP5

With the development of computer technology, there are more and more various programming languages, among which PHP language is a programming language widely used in the field of Web development. PHP is mainly used for server-side programming. It can generate dynamic web page content, realize data interaction with databases, and process forms, etc. During the development of the PHP language, many versions have appeared, among which PHP 5 and PHP 7 are the two most commonly used versions. This article will explore the syntax differences between PHP 7 and PHP 5.

1. Error handling

PHP 5 and PHP 7 have certain differences in error handling methods. In PHP 5, error handling is mainly through error levels, namely E_ERROR, E_WARNING, E_PARSE, E_NOTICE, E_STRICT and E_DEPRECATED. In PHP 7, a new error level has been added: E_RECOVERABLE_ERROR. In response to this error, PHP 7 has been replaced with a fatal error, which means that when the E_RECOVERABLE_ERROR error occurs in the program, the program will terminate and no output will be produced.

2. Types

Another major difference between PHP 5 and PHP 7 is types. In PHP 5, type hints are optional, which means a variable can hold a value of any type. In PHP 7, strict typing was introduced, which means that function or method parameters must strictly match the expected type. If the types do not match, a fatal error is generated and the program is terminated.

For example, in PHP 5, the following code can run normally:

function add($a, $b) {
    return $a + $b;
}

$x = add(2, "3");

In the above example, $a and $b can hold any type of value, including integers and String. Therefore, add(2, "3") is also legal and will return the number 5. However, in PHP 7, the following code is not allowed:

declare(strict_types=1);

function add(int $a, int $b) {
    return $a + $b;
}

$x = add(2, "3");

This is because in PHP 7, we tell the compiler that the type of the parameter should be int instead of Any type. Therefore, add(2, "3") is not legal and will generate a fatal error, thus terminating the program.

3. Performance

One of the biggest advantages of PHP 7 is its performance improvement. Compared to PHP 5, PHP 7 can improve application performance up to twice. This is mainly because PHP 7 introduces a new virtual machine engine: Zend Engine 3.0. Compared with the virtual machine engine of PHP 5, Zend Engine 3.0 has higher performance and better optimization of memory management.

4. New operators

PHP 7 introduces some new operators in syntax, making the code more concise and readable. Among them, one of the most commonly used new operators is the null coalescing operator (??). This operator can be used to determine whether a variable is null. If it is null, return another given value, otherwise return the variable's own value. For example, in the following code, the variable $name outputs $name if it exists, otherwise it outputs the string "Anonymous":

echo $name ?? "Anonymous";

Another commonly used new operator is the combined comparison operator (<=> ;), this operator can compare the size of two variables and return three different values ​​-1, 0 or 1. For example:

echo 1 <=> 2; //输出-1
echo 2 <=> 2; //输出0
echo 3 <=> 2; //输出1

Summary
To sum up, the syntactic differences between PHP 7 and PHP 5 are mainly reflected in error handling, types, performance and new operators. Although there are certain differences in syntax between PHP 7 and PHP 5, for most developers, these changes will not have a big impact on existing PHP code. Developers can choose a suitable version according to their project needs and maximize the advantages of the PHP language. 
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