How to call method which accepts slice of interface as parameters in golang?

Question

I want to call a method which accepts slice of interface as paramers in golang, but I find that I cannot pass it write as this:

type Base interface {
    Run()
}

type A struct {
    name string
}

func (a *A) Run() {
    fmt.Printf("%s is running\n", a.name)
}

func foo1(b Base) {
    b.Run()
}

func foo2(s []Base) {
    for _, b := range s {
        b.Run()
    }
}

func TestInterface(t *testing.T) {
    dog := &A{name: "a dog"}
    foo1(dog)
    // cat := A{name: "a cat"}
    // foo1(cat)
    s := []*A{dog}
    foo2(s)
}

I get error like this:

cannot use s (type []*A) as type []Base in argument to foo2

from the FAQ: https://golang.org/doc/faq#convert_slice_of_interface — JimB, Jun 01 '17 at 17:07

score 5 · Accepted Answer · answered Jun 01 '17 at 17:12

If the function takes a []Base parameter, you must pass a []Base parameter. Not a []interface{}, not a []thingThatImplementsBase, but specifically a []Base. A slice of interfaces isn't an interface - it isn't "implemented by" a slice of any other type. The elements of a slice of interfaces can be anything that implements the interface, but the slice itself is of a strict and specific type.

How to call method which accepts slice of interface as parameters in golang?

1 Answers1