Try to understand handler functions in Go

php editor banana introduction: The processing function in the Go language is an important concept. It is a special type of function used to process and respond to requests from the client. Understanding how handler functions work is critical to developing efficient network applications. This article will delve into the concept and usage of processing functions to help readers better understand processing functions in the Go language. By reading this article, readers will understand important knowledge points such as how to define processing functions, parameters and return values ​​of processing functions, and the execution order of processing functions, laying a solid foundation for developing high-performance network applications. Whether you are a beginner or an experienced developer, this article will take you step by step to master the essence of processing functions in the Go language.

Question content

I'm trying to do this exercise from the Golang documentation: https://go.dev/doc/articles/wiki/, but I don't understand something. In the second part of the article, when we started using the "net/http" package, we wrote this (I left the more complete code here: https://go.dev/doc/articles/wiki/ part2.go):

func viewHandler(w http.ResponseWriter, r *http.Request) {

    title := r.URL.Path[len("/view/"):]

    p, _ := loadPage(title)

    fmt.Fprintf(w, "<h1 id="s">%s</h1><div>%s</div>", p.Title, p.Body)

}


func main() {

    http.HandleFunc("/view/", viewHandler)

    log.Fatal(http.ListenAndServe(":8080", nil))

}

I don't understand why the viewHandler is in the parameters of http.HandleFunc without the two parameters defined above. Because there are two parameters in the definition of viewHandler: w and r? When/who is done?

Solution

Go supports using function signatures as parameters of other functions. This is a powerful feature in Go called "First-Class Functions".

In Go, functions are first-class citizens, which means you can pass functions as arguments to other functions and even return functions from functions. This feature is particularly useful for creating higher-order functions and handling callbacks.

Here is a shorter example:

type BinaryOperation func(int, int) int

func Apply(operation BinaryOperation) int {
    return operation(5, 5)
}

func main() {
    // Define an addition function inline
    sum := Apply(func(a, b int) int { return a + b })
    fmt.Println(sum) // 10

    // Define a subtraction function inline
    difference := Apply(func(a, b int) int { return a - b })
    fmt.Println(difference) // 0
}

In addition, understanding the concept of callbacks will help you understand this code.

Callbacks are a common programming concept that involves passing a function as a parameter to another function and executing that function when a specific event occurs or a specific condition is met. Callbacks are usually used to implement asynchronous operations, event processing, and scheduled tasks.

A simple callback example:

func eventHandler(event string, callback func(string)) {
    fmt.Println("Event:", event)
    callback(event)
}

func main() {
    eventHandler("Button Click", func(event string) {
        fmt.Println("Handling", event)
    })

    eventHandler("File Save", func(event string) {
        fmt.Println("Saving", event)
    })
}

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