How to use constants and enumeration types in Go language?

How to use constants and enumeration types in Go language?

In programming languages, constants and enumeration types are very important concepts. A constant is a fixed value that will not change during the running of the program. An enumeration type is a group of named constants that are used in the program. is used to represent a fixed set of values. The Go language also supports constants and enumeration types, and their use will be described in detail below.

Constant

Constant in the Go language can be defined with the const keyword. The syntax format is as follows:

const identifier [type] = value

Among them, identifier represents the constant name, type represents the constant type, and value represents The value of the constant. Constants cannot be modified again after they are defined and can be used throughout the program.

For example:

package main

import "fmt"

const (
    Pie   = 3.14
    Count = 10
)

func main() {
    fmt.Printf("Pie: %v
", Pie)
    fmt.Printf("Count: %v
", Count)
}

In the above example, we defined two constants Pie and Count and output their values ​​in the main function. The output result is:

Pie: 3.14
Count: 10

When defining a constant, if no specific numerical type is specified for the type, the Go language will automatically select the appropriate type based on the type of the constant value. For example:

const (
    i = 5        // int 类型
    j = "hello"  // string 类型
    k = 8.22     // float64 类型
)

func main() {
    fmt.Printf("i: %v, j: %v, k: %v
", i, j, k)
}

The output result is:

i: 5, j: hello, k: 8.22

Enumeration type

There is no special enumeration type in the Go language, but we can use const to define a group of named constant to represent a fixed set of values. For example:

package main

import "fmt"

const (
    Monday    = 0
    Tuesday   = 1
    Wednesday = 2
    Thursday  = 3
    Friday    = 4
    Saturday  = 5
    Sunday    = 6
)

func main() {
    fmt.Printf("Monday: %v
", Monday)
    fmt.Printf("Tuesday: %v
", Tuesday)
    fmt.Printf("Wednesday: %v
", Wednesday)
    fmt.Printf("Thursday: %v
", Thursday)
    fmt.Printf("Friday: %v
", Friday)
    fmt.Printf("Saturday: %v
", Saturday)
    fmt.Printf("Sunday: %v
", Sunday)
}

In the above example, we use const to define a set of constants to represent each day of the week, and output the value of each constant in the main function. The output result is:

Monday: 0
Tuesday: 1
Wednesday: 2
Thursday: 3
Friday: 4
Saturday: 5
Sunday: 6

In addition to using const to define a set of constants to represent the enumeration type, we can also use iota to define a set of continuous constants to represent the enumeration type. For example:

package main

import "fmt"

const (
    Monday = iota
    Tuesday
    Wednesday
    Thursday
    Friday
    Saturday
    Sunday
)

func main() {
    fmt.Printf("Monday: %v
", Monday)
    fmt.Printf("Tuesday: %v
", Tuesday)
    fmt.Printf("Wednesday: %v
", Wednesday)
    fmt.Printf("Thursday: %v
", Thursday)
    fmt.Printf("Friday: %v
", Friday)
    fmt.Printf("Saturday: %v
", Saturday)
    fmt.Printf("Sunday: %v
", Sunday)
}

In the above example, we use iota to define a set of continuous constants to represent each day of the week, and output the value of each constant in the main function. The output is the same as the previous example.

Summary

In the Go language, constants and enumeration types are very important concepts. They can help us create fixed values ​​and types and improve the readability and maintainability of the program. . When using constants and enumeration types, we need to pay attention to the fact that constants cannot be modified after they are defined, and we need to consider the scope of their scope.

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