This Go program demonstrates the concept of composition in Go structs, where a struct includes another struct as a field. It also showcases method overriding through embedding and interface implementation. Let's go through each part of the code with inline comments and additional explanations:
package main
import "fmt"
// Define a struct named 'base' with a field 'num'
type base struct {
num int
}
// Method 'describe' for the 'base' struct, returns a string describing the base struct
func (b base) describe() string {
return fmt.Sprintf("base with num=%v", b.num)
}
// Define a struct named 'container' that embeds the 'base' struct and has an additional field 'str'
type container struct {
base // Embedding the 'base' struct
str string
}
func main() {
// Create an instance of the 'container' struct with field values
co := container{
base: base{
num: 1,
},
str: "some name",
}
// Print the values of the 'container' struct fields
fmt.Printf("co={num: %v, str: %v}\n", co.num, co.str)
// Access the 'num' field of the embedded 'base' struct directly
fmt.Println("also num:", co.base.num)
// Call the 'describe' method on the 'container' struct, which internally calls the 'describe' method of the embedded 'base' struct
fmt.Println("describe:", co.describe())
// Define an interface named 'describer' with a 'describe' method
type describer interface {
describe() string
}
// Create a variable 'd' of type 'describer' and assign the 'container' struct to it
var d describer = co
// Call the 'describe' method on the 'describer' interface, which calls the overridden method in the 'container' struct
fmt.Println("describer:", d.describe())
}
co={num: 1, str: some name}
also num: 1
describe: base with num=1
describer: base with num=1
Explanation:
-
The
base
struct has a single field,num
, and a method calleddescribe
that returns a string describing the base struct. -
The
container
struct embeds thebase
struct, effectively inheriting its fields and methods. It also has an additional field,str
. -
In the
main
function:- An instance
co
of thecontainer
struct is created with field values. - Field values of the
container
struct are printed, and the embeddedbase
struct field (num
) is accessed directly. - The
describe
method is called on thecontainer
struct, which internally calls thedescribe
method of the embeddedbase
struct. - An interface named
describer
is defined with adescribe
method. - A variable
d
of typedescriber
is created and assigned thecontainer
struct. - The
describe
method is called on thedescriber
interface, demonstrating method overriding. The overridden method in thecontainer
struct is called.
- An instance