How can functions and types be used to fulfill the requirements of an interface?

Function implementing interface

Question:

How do functions and types interact in an interface?

Answer:

An interface defines the required methods for a type to implement. Here's an example:

type Handler interface {
    ServeHTTP(*Conn, *Request)
}

Example 1: Custom type implementing interface

type Counter int

func (ctr *Counter) ServeHTTP(c *http.Conn, req *http.Request) {
    fmt.Fprintf(c, "counter = %d\n", ctr)
    ctr++
}

The Counter type implements the ServeHTTP method, satisfying the Handler interface.

Example 2: Utilizing HandlerFunc (function as a receiver)

type HandlerFunc func(*Conn, *Request)

func (f HandlerFunc) ServeHTTP(c *Conn, req *Request) {
    f(c, req)
}

var Handle404 = HandlerFunc(notFound)

Here, a HandlerFunc is a function taking a Conn and Request and returning nothing. This allows functions like notFound to be used as a handler by adding a ServeHTTP method to them through HandlerFunc. This indirect method allows for flexibility in implementing the interface.

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