Explain the use of Go's constant expressions for defining constant values?

In Go, constant expressions are used for defining values that cannot be changed during program execution. Constant expressions are evaluated at compile time, and their values are determined based on the values of other constant expressions or literals.

Constant expressions can be used to define numeric, string, and boolean values. Numeric constant expressions can be of different types, such as int, float, and complex. String constant expressions can be used to define string literals, and boolean constant expressions can be used to define true or false values.

One of the advantages of using constant expressions in Go is that they can be used in contexts where values are required, such as array sizes or switch cases. For example, the following code snippet defines an array of size 10 using a constant expression:

const size = 10
var array [size]int

This code defines a constant **size** with a value of 10, and then creates an array of integers with that size.

Constant expressions can also be used in switch statements to define case expressions. For example, the following code snippet defines a switch statement with three cases, each using a different constant expression:

const (
    first = iota
    second
    third
)

switch i {
case first:
    // do something
case second:
    // do something else
case third:
    // do something different
}

In this code, the constants **first**, **second**, and **third** are defined using the **iota** keyword, which generates a sequence of incrementing integer values. These constants are then used as case expressions in the switch statement.

Overall, constant expressions are a useful tool for defining values that are known at compile time and cannot be changed during program execution. They can be used in a variety of contexts to improve code readability and maintainability.