Go接口值是实现该接口的整个变量吗？

Question

New to Go here. I was taking a tour of Go and came across one word that I was confused what it was.

It's the 11th page of the Method section here. It says, "interface values can be thought of as a tuple of a value and a concrete type."

My understanding is that an interface value is a variable that implements that interface. E.g.:

type Animal interface {
    run()
}

type Cat struct { … }

func main() {
    kitty := Cat{ … }
}

func (c Cat) run() { … }

Is kitty an interface value?

Answer 1

In your case since you used short variable declaration to create kitty, the type is inferred from the right-hand side expression, and type of kitty will be the concrete type Cat.

But since the Cat concrete type (non-interface type) implements the Animal interface type, you may assign a value of Cat to a variable whose type is Animal, like in this example:

kitty := Cat{}
var kitty2 Animal = kitty

"Implements" by spec means:

An interface type specifies a method set called its interface. A variable of interface type can store a value of any type with a method set that is any superset of the interface. Such a type is said to implement the interface.

Interface values, schemantically, contain a (value; type) pair, being the value stored in them, and their concrete type.

For more details about interface internals, read blog post: The Go Blog: The Laws of Reflection
And Go Data Structures: Interfaces (by Russ Cox).

For an introduction why interfaces are needed or how / when to use them, see Why are interfaces needed in Golang?