Let's talk about the role of var keyword in Golang

With the continuous development of Golang, more and more developers have joined the Golang camp. In the daily development process, the use of variables is a very critical aspect. In Golang, the declaration and use of variables are more special and flexible, and the var keyword is a frequently used way to declare variables. In this article, we will discuss the role of var keyword in Golang and whether variables declared with var are readable and writable.

The role of the var keyword

In Golang programs, use the var keyword to declare variables or initialize variables with the := operator. In Golang, the var keyword can be used to declare variables inside and outside functions, providing high flexibility.

First, let’s take a look at the use of the var keyword inside a function. Within a function, use the var keyword to declare local variables, whose scope is limited to the function. For example:

func main() {
    var count int
    count = 10
    fmt.Println(count)
}

In the above code, a variable named count is declared using the var keyword and initialized to 0. In the next line of code, we assign count to 10 and print the output. It should be noted that if we do not initialize it explicitly, Golang will help us automatically initialize the variable to a zero value (0, false or empty string).

In addition to using the var keyword to declare variables inside a function, we can also use it outside the function to declare global variables. For example:

var message string = "Hello World!"

func main() {
    fmt.Println(message)
}

In the above code, we declare a global variable named message using the var keyword outside the function and initialize it to the string "Hello World!". Inside the main function, we print out this global variable. It should be noted that using the var keyword to declare variables outside a function has higher visibility, and the variables defined can be used by any part of the program.

Whether the variable declared by var is read-only

Variables declared using the var keyword in Golang are readable and writable by default. That is, we can modify the values ​​of these variables in any part of the program. For example:

func main() {
    var count int = 10
    fmt.Println(count)

    count = 20
    fmt.Println(count)
}

In the above code, we first declare a variable named count using the var keyword and initialize it to 10. In the rest of the program, we change the value of count to 20. This shows that the variable declared by var is not a read-only variable and its value can be modified arbitrarily in the program.

However, in certain scenarios, we can also use the const keyword to declare read-only variables. For example:

const count int = 10

func main() {
    fmt.Println(count)

    count = 20
    fmt.Println(count)
}

In the above code, we declared a read-only variable named count using the const keyword and initialized it to 10. In the subsequent code of the program, we try to change the value of count to 20, and we will find that the compiler will prompt an error: "cannot assign to count". This is because the count variable we declared is read-only and cannot be modified in the program.

Summary

In Golang programs, the var keyword is a frequently used way to declare variables, and its scope of use can include local variables and global variables. By default, variables declared with var are readable and writable and can be modified in any part of the program. The const keyword is used to declare read-only variables that cannot be modified in the program. By deeply understanding the usage of the var keyword and the characteristics of variable declarations, we can develop Golang programs more efficiently and improve development efficiency.

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