Detailed explanation of curried function in Vue3: a better way of functional programming

Detailed explanation of the curried function in Vue3: a better functional programming approach

In functional programming, currying is a common technique. The Vue3 framework also introduces support for curried functions, providing a better functional programming approach. In this article, we will introduce the curried functions in Vue3 in detail to help you better understand and use them.

1. What is currying?

Currying refers to the process of converting a function with multiple parameters into a series of functions that only receive a single parameter. This converted function is called a curried function. Through currying, we can convert functions with multiple parameters into multiple unary functions, which makes function combination more flexible.

For example, we have a function that needs to be passed two parameters:

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

We can use currying to convert this into a function that receives one parameter and returns a function that receives another parameter:

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

2. Problems with the previous functional programming method

Before Vue3, when we used functional programming, we may encounter the following problems:

a. Arguments transfer problem

First look at the following function:

function foo(a, b, c) {
  // ...
}

If we want to use currying to convert this function, we can create a function for each parameter, As shown below:

const curriedFoo = a => b => c => foo(a, b, c);

Now we can pass each parameter separately through curriedFoo to call the function, for example:

curriedFoo(1)(2)(3)

This calling method seems normal, but there is actually a problem: If we accidentally pass an extra parameter, for example:

curriedFoo(1)(2)(3)(4)

This call will not generate a compile-time error, but an error will occur at runtime. This is because in the curried function, each call returns a new function that accepts a single parameter. If we accidentally pass multiple parameters in the last call, an error will occur.

b. Difficulty using Lambda expressions

Before Vue3, we may encounter the following problems when using Lambda expressions:

Have multiple parameters Lambda expressions are difficult to handle. For example:

const foo = (a, b, c) => {...};

How to convert it into a Lambda expression or function that receives a single parameter?

3. Solution to the currying function in Vue3

In order to solve the above problems, Vue3 provides a new curried function to better support functional programming.

The curried function is a higher-order function that receives a function as a parameter and returns a new function. This new function allows us to use currying to call the passed-in function without accidentally passing it. Problem with multiple parameters. For example:

import {curried} from 'vue';

// 普通函数
function foo(a, b, c) {
  return a + b + c; 
}

// curried函数
const curriedFoo = curried(foo);

// 调用curried函数
curriedFoo(1)(2)(3); // 6
curriedFoo(1)(2, 3); // 6

In addition to the above application methods, the curried function also supports two special calling methods. One is to partially apply a certain parameter, for example:

curriedFoo(1)(2) // 返回一个接收单一参数的函数

const fooPartial = curriedFoo(1);
fooPartial(2)(3); // 6

The other is to reverse some parameters, for example:

const curriedFooReversed = curried(foo, true);
curriedFooReversed(3)(2)(1); // 6

In the statement curried(foo, true), the second parameter true indicates reversing the order of the parameters.

4. Summary

The curried function in Vue3 provides us with a better functional programming method. Through the currying function, we can combine functions more flexibly, and we no longer need to worry about passing parameters when calling the function. Whether in actual development or in the process of learning functional programming, curried functions are a technology worth mastering and using.

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