What are interfaces used for in Go?

In Go, interfaces define a set of methods that a type must implement in order to satisfy the interface. Interfaces enable a high degree of flexibility and polymorphism in Go code, allowing developers to write more modular and extensible programs.

An interface is declared using the **interface** keyword, followed by the list of method signatures that must be implemented by any type that satisfies the interface. Here's an example:

type Shape interface {
    Area() float64
    Perimeter() float64
}

This interface, called **Shape**, defines two methods: **Area** and **Perimeter**. Any type that implements these two methods can be considered a **Shape**.

For example, we can define a **Circle** type that satisfies the **Shape** interface:

type Circle struct {
    Radius float64
}

func (c Circle) Area() float64 {
    return math.Pi * c.Radius * c.Radius
}

func (c Circle) Perimeter() float64 {
    return 2 * math.Pi * c.Radius
}

In this example, the **Circle** type has an **Area** method and a **Perimeter** method, both of which have the appropriate method signature to satisfy the **Shape** interface. Therefore, we can say that **Circle** is a **Shape**.

Interfaces in Go can also be used in a variety of other ways, such as embedding interfaces within other interfaces, and using interfaces as function parameters and return types. Overall, interfaces are a powerful feature of Go that enable developers to write more modular and extensible code.