A first look at functional programming in PHP

Functional Programming (Functional Programming) is a programming paradigm whose concept is derived from lambda calculus. It constructs complex calculation processes by combining, transforming, abstracting and other operations on functions. Different from traditional imperative programming (Imperative Programming), functional programming emphasizes the immutability and reusability of functions, thereby improving the readability and maintainability of the code. Currently, more and more programming languages ​​are beginning to support functional programming, and PHP is no exception.

This article will introduce some basic features and common functions of functional programming in PHP. I hope readers can understand the basic concepts and applications of functional programming through this article.

1. The basic idea of ​​functional programming

The basic idea of ​​functional programming is that the operation of a function does not depend on the state during operation. That is to say, the input of the function determines the output. Similarly The input will always get the same output, and will not be interfered by external variables.

A simple example:

function add($x, $y) {
  return $x + $y;
}

Obviously, the output of the above function is only affected by the input $x and $y, and is not affected by any other state, so this is a typical Functional programming examples.

2. Functional programming in PHP

The tools that support functional programming in PHP mainly include anonymous functions and higher-order functions.

Anonymous function

Anonymous function refers to a function without a function name, also called a Lambda function. In PHP, anonymous functions can be defined by using the "function(){}" syntax.

For example:

$add = function($x, $y) {
  return $x + $y;
};

echo $add(1, 2); // 输出 3

Higher-order function

Higher-order function refers to a function that receives one or more functions as parameters and returns a new function. Functions such as array_map, array_filter, and array_reduce in PHP are all high-order functions.

array_map function

array_map function is a function often used in functional programming. Its function is to apply a specified function to each element in an array and return a new array. For example:

$a = [1, 2, 3];

$b = array_map(function($item) {
  return $item * 2;
}, $a);

print_r($b); // 输出 [2, 4, 6]

array_filter function

array_filter function is to filter the elements in an array and return a new array. For example:

$a = [1, 2, 3, 4];

$b = array_filter($a, function($item) {
  return $item % 2 == 0;
});

print_r($b); // 输出 [2, 4]

3. Application examples

Functional programming greatly improves the readability and maintainability of the code, and is also suitable for some simple data processing, conversion and other scenarios.

As a simple example, suppose we want to perform the following operations on an array:

• Convert the array into a string and specify the delimiter;
• According to Specify the character to split the string and get a new array;
• Perform some operations on each element in the new array.

Using functional programming, this process can be easily implemented:

$a = [1, 2, 3];

$result = implode(':', $a) // 将数组转化为字符串，并指定分隔符
  |> explode(':', $result) // 分割字符串，得到新数组
  |> array_map(function($item) {
    return $item * 2; // 对每个元素进行操作
  }, $result);

print_r($result); // 输出 [2, 4, 6]

In the above code, we use the |> (pipeline) operator to connect each operation , realizing pipeline processing of data.

4. Summary

This article introduces some basic features and common functions of functional programming in PHP, including anonymous functions, higher-order functions, array_map, array_filter, etc.

It is worth mentioning that PHP 8 also adds some new features of functional programming, such as nullsafe operator, new pipe operator, automatic property expansion, etc. These features can greatly improve functional programming. efficiency and convenience.

In practice, functional programming does not completely replace traditional imperative programming, but the two programming paradigms complement each other to achieve more convenient and efficient development. Therefore, it is recommended that developers reasonably use functional programming ideas and tools according to actual conditions in actual development to raise the standardization, readability, and maintainability of the code to a new level.

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