golang const usage

The const keyword in golang is used to define constants, and their values ​​will not change when the program is running. Constants can be numeric, character or string, Boolean and other types.

Definition form: const constant name type = value

The constant name and type are required, but the value is optional. If no value is assigned, Go will automatically assign a default value to the constant. For example, the default value of numeric constants is 0, the default value of Boolean constants is false, and the default value of string constants is the empty string.

The advantage of using constants is that you can avoid hard coding in the code and increase the readability and maintainability of the program. In golang, constants also have the following characteristics:

1. Constants must be initialized when declared.
2. Constants can only be used inside functions and packages.
3. Constants can be used with expressions, for example: const c = a b.
4. Constants can be passed as actual parameters of functions.
5. The difference between constants and variables is that the value of a constant cannot be modified.

Definition of constants

There are two ways to define constants in golang:

1. Use the const keyword

const Pi float32 = 3.14159265359

const Name string = "John"

const Age int = 25

2. Use iota keyword

iota is a built-in constant generator in the golang language. In a const declaration, iota is initialized to 0 and is automatically incremented by 1 each time it is used on a new line.

The following is a simple example of an iota constant:

const (

Monday = iota // 0
Tuesday       // 1
Wednesday     // 2
Thursday      // 3
Friday        // 4
Saturday      // 5
Sunday        // 6

)

In the above example, Monday has a value of 0 and Tuesday The value is 1, and so on.

iota can also be used for automatic numbering of enumeration constants, for example:

const (

Apple = iota
Banana
Cherry
Durian

)

In the above example, Apple's has a value of 0, Banana has a value of 1, and so on.

Use of constants

The use of constants is similar to variables, just write the constant name directly. For example:

const Pi = 3.1416
r := 2.0
area := Pi r r

In the above example, the value of the constant Pi is 3.1416, the value of r is 2.0, and the value of area is 12.5664.

Constants defined inside a function are only visible inside the function, while constants defined inside a package can be accessed throughout the package, for example:

package main

import "fmt"

const (

Monday = "星期一"
Tuesday = "星期二"
Wednesday = "星期三"
Thursday = "星期四"
Friday = "星期五"
Saturday = "星期六"
Sunday = "星期日"

)

func main() {

fmt.Println("今天是",Monday)

}

Summary

This article introduces the usage of the const keyword in golang, including the definition, use and characteristics of constants. Constants are immutable values ​​in Golang programs, which avoid hard coding and improve the readability and maintainability of the program.

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