Can Go Implement Anonymous Interfaces?

Is Anonymous Interface Implementation Possible in Go?

Consider the following interface and a function from an imaginary library:

type NumOp interface {
    Binary(int, int) int
    Ternary(int, int, int) int
}

func RandomNumOp(op NumOp) {
    // ...
}

To implement this interface, one could define a type like:

type MyAdd struct {}
func (MyAdd) Binary(a, b int) int {return a + b }
func (MyAdd) Ternary(a, b, c int) int {return a + b + c }

Need for a Functional Implementation

However, suppose we need to implement the interface using anonymous functions for single-use scenarios. This would allow us to write:

RandomNumOp({
   Binary: func(a,b int) int { return a+b},
   Ternary: func(a,b,c int) int {return a+b+c},
})

Implementation Restrictions

Unfortunately, in Go, method declarations must reside at the file level. To implement an interface with multiple methods, these declarations are required.

Workable Implementation

If a working implementation is necessary, you can use a dummy implementation:

type DummyOp struct{}

func (DummyOp) Binary(_, _ int) int     { return 0 }
func (DummyOp) Ternary(_, _, _ int) int { return 0 }

Dynamic Partial Implementation

To set some methods dynamically, consider a delegator struct:

type CustomOp struct {
    binary  func(int, int) int
    ternary func(int, int, int) int
}

func (cop CustomOp) Binary(a, b int) int {
    // ...
}

func (cop CustomOp) Ternary(a, b, c int) int {
    // ...
}

Non-Functional Implementation

If the methods don't need to be callable, you can use an anonymous struct literal:

var op NumOp = struct{ NumOp }{}

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