What is polymorphism in Go?

Overview

Polymorphism is an ability of a thing to be displayed in multiple forms. For example, a human can be a child, an adult, a sibling, a parent, and so on. Thus, the same human exhibits different forms based on situations, and this is what we call polymorphism.

In a more technical term, polymorphism can be defined as a function that can be used for different types. However, that function must have different signatures.

Example

In Go, we can implement polymorphism using interfaces only.

Let's see an example in the code snippet below:

package main
// importing package 'fmt'
import "fmt"
// creating an interface 'Language'
type Language interface {
    getDevelopedBy() string
}
// creating a structure 'JavaScript'
// that contains the fields required by interface 'Language'
type JavaScript struct {
    DevelopedBy string
}
// implementing methods of interface 'Language'
// for structure 'JavaScript'
func (javaScript JavaScript) getDevelopedBy() string {
    return javaScript.DevelopedBy;
}
// creating a structure 'Python' 
// that contains the fields required by interface 'Language'
type Python struct {
    DevelopedBy string
}
// implementing methods of interface 'Language'
// for structure 'Python'
func (python Python) getDevelopedBy() string {
    return python.DevelopedBy;
}
func main() {
    // creating an instance of interface 'Language'
    var ILanguage Language
    // creating an object of structure 'JavaScript'
    javaScript := JavaScript{DevelopedBy: "Brendan Eich"}
    // creating an object of structure 'Python'
    python := Python{DevelopedBy: "Guido van Rossum"}
    // assigning object 'javaScript' to 'ILanguage'
    // and invoking getDevelopedBy()
    ILanguage = javaScript
    fmt.Println(ILanguage.getDevelopedBy())
    // assigning object 'python' to 'ILanguage' 
    // and invoking getDevelopedBy()
    ILanguage = python
    fmt.Println(ILanguage.getDevelopedBy())
}

Explanation

Line 3: We import the package fmt.
Line 6–9: We create an interface Language.
Line 13–15: We create a structure JavaScript.
Line 19–21: We implement the methods of the Language interface for the JavaScript structure.
Line 25–27: We create a structure Python.
Line 19–21: We implement the methods of the interface Language for the structure Python.
Line 37: We create an instance of the interface Language.
Line 40: We create an object of the structure JavaScript.
Line 43: We create an object of the structure Python.
Line 47–48: We assign the object javaScript to ILanguage and invoke the function getDevelopedBy().
Line 52–53: We assign the object python to ILanguage and invoke the function getDevelopedBy().

Output

Here, we have created two objects of structures JavaScript and Python, respectively. Both implement the interface Language.
When we run the code, both these objects will invoke the function getDevelopedBy() and will display the DevelopedBy value on the console.

Since only one method was used for different objects, we can be sure that this is an example of polymorphism. Even if we add more types and implement the interface Language for each of them, they will be able to invoke the function getDevelopedBy() due to polymorphism.

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