How Can I Avoid Redundant Method Implementations for Different Types Using Interfaces in Go?

Implementing Common Methods for Different Types Using Interfaces

In Go, interfaces provide a powerful mechanism for defining contracts that multiple types can implement. However, it can sometimes seem redundant to implement similar methods for multiple types implementing the same interface.

To address this, let's consider the example of two structs, First and Second, which both contain a string field named str. We want both structs to implement an interface A that defines a PrintStr() method for printing the value of str.

Initially, it might seem natural to define separate implementations for First and Second, as follows:

type First struct {
    str string
}

func (f First) PrintStr() {
    fmt.Print(f.str)
}

type Second struct {
    str string
}

func (s Second) PrintStr() {
    fmt.Print(s.str)
}

However, this approach is indeed repetitive. To avoid redundancy, we can instead leverage a compositional approach. We can define a base type WithString that contains the common functionality and embed it into both First and Second structs. This allows us to define the PrintStr() method only once in the base type:

type WithString struct {
    str string
}

func (w WithString) PrintStr() {
    fmt.Print(w.str)
}

type First struct {
    WithString
}

type Second struct {
    WithString
}

type A interface {
    PrintStr()
}

This technique effectively decouples the implementation of the PrintStr() method from the specific types First and Second, resulting in a more concise and maintainable codebase.

For instance, given the following usage:

a := First{
    WithString: WithString{
        str: "foo",
    },
}

Calling a.PrintStr() will print "foo" because First embeds the WithString type, which provides the PrintStr() implementation.

By utilizing composition and interfaces, Go allows us to create type hierarchies where different types can share common functionality without the need for redundant code.

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