如何将接口传递给具有大量参数的方法

Question

I had written a lazy code to demonstrate the issue I am having to implement interfaces. I have methods M1, M2 that take struct X as an argument and have a type of struct Y. I wanted all these methods to be implemented by a single interface I. The issue is the method M that implements the interface I needs to be aware of the arguments that are required to be passed to the child methods (M1,M2). I get an error: <argument name> used as a value when I pass multiple arguments in M

type Y struct {
 a int
}

type X struct {
 a int
}

(y *Y) func M1(x X) struct {
 return y.a+x.a
}

(y *Y) func M2(x X) struct {
 return y.a*x.a
}

type I interface {
 M1(x X)
 M2(x X)
}

func M(i I, x X) {
 fmt.println(i.M1(x)) //returns an error i.M1(x) used as a value
 fmt.println(i.M2(x)) //returns an error i.M2(x) used as a value
}

Answer 1

The problem that cause <argument name> used as a value error in your example is that functions that form interface I are declared to have no return value:

type I interface {
 M1(x X)
 M2(x X)
}

Surely you can't pass function-call as argument of Println if the function returns nothing: fmt.println(i.M1(x)). Change the interface declaration in your example to return something (and a few more fixes*):

type Y struct {
 a int
}

type X struct {
 a int
}

func(y *Y) M1(x X) int {
 return y.a+x.a
}

func(y *Y) M2(x X) int {
 return y.a*x.a
}

type I interface {
 M1(x X) int
 M2(x X) int
}

func M(i I, x X) {
 fmt.Println(i.M1(x))
 fmt.Println(i.M2(x))
}

<kbd>playground</kbd>

*) change M1 & M2 to return int instead of struct and fix syntax for function declaration with receiver