How to use constants in Go?

In Go, constants (Constants) are identifiers that maintain a fixed value and do not change throughout the execution of the program. Constants in Go are declared using the const keyword. In this article, we will explore how to use constants in Go.

1. How to declare a constant

Declaring a constant in Go is very simple, just use the const keyword. The format is as follows:

const identifier [type] = value

Among them, identifier is the constant name, [type] is the optional constant data type, and value is the constant value.

They are defined as follows:

• identifier: The name of the constant, conforming to Go's identifier rules.
• type: Data type of constant. If not defined, Go will automatically deduce the data type of the constant.
• value: The value of the constant. The value of a constant can be a primitive type, an object (such as a string), or a function. Constant values ​​must be determined at compile time.

For example, here are a few examples of declaring constants:

const pi = 3.14159
const age int = 18
const name string = "Lucy"

2. Using constants in functions

Constants can be declared inside functions and use. There is no difference between declaring and using constants inside a function and declaring and using them outside the function.

For example, the following is a function that uses constants:

func printCircleArea(radius float64) {
    const pi = 3.14159
    area := pi * (radius * radius)
    fmt.Printf("The area of the circle is: %f
", area)
}

In this function, we declare a constant pi and then calculate the area of ​​a circle. No matter how many times the function is called, the value of the constant pi is always 3.14159.

3. Enumeration of constants

In Go, constants can also be used to define enumerations. An enumeration is a set of named constants whose values ​​increase one by one. In Go, we can use the iota keyword to define enumerations.

iota is a counter of enumeration constants. When defining the enumeration, each constant will be automatically assigned an integer. The initial value of the integer is 0. Every time iota appears, its value is automatically increased by 1.

For example, the following are some examples of defining enumerations:

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

In this example, we define some enumeration constants whose values ​​range from 0 to 6.

We can also "enumerate" our own values ​​by skipping a certain constant:

const (
    Unknown = 0
    Female  = 1
    Male    = 2
)

In this example, we assign Unknown to 0, and the following two constants are Assign values ​​1 and 2. This is because we only used iota after the first constant, which means the value of iota is reinitialized to 0 in the next ConstSpec.

4. Notes on constants

• Constant values ​​can only be assigned once. Once assigned, it cannot be changed.
• Constant must be initialized when declared. Uninitialized constants cannot be used.
• Constant cannot be declared inside a function.
• Constant can be a basic type, object (such as string) or function.
• Constant does not need to use the := operator when declaring it.

5. Summary

In this article, we discussed various ways of using constants in Go. We saw how to declare constants, how to use them in functions, and how to use constants to define enumerations. We also discussed some considerations about using constants in Go.

Constants are a very powerful tool that make your code safer and easier to maintain. I hope this article helps you a lot when learning Go.

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