Comment by dilap
This has already been explained many times, but it's so much fun I'll do it again. :-)
So: The way Go presents it is confusing, but this behavior makes sense, is correct, will never be changed, and is undoubtedly depended on by correct programs.
The confusing thing for people use to C++ or C# or Java or Python or most other languages is that in Go nil is a perfectly valid pointer receiver for a method to have. The method resolution lookup happens statically at compile time, and as long as the method doesn't try to deref the pointer, all good.
It still works if you assign to an interface.
package main
import "fmt"
type Dog struct {}
type Cat struct {}
type Animal interface {
MakeNoise()
}
func (*Dog) MakeNoise() { fmt.Println("bark") }
func (*Cat) MakeNoise() { fmt.Println("meow") }
func main() {
var d *Dog = nil
var c *Cat = nil
var i Animal = d
var j Animal = c
d.MakeNoise()
c.MakeNoise()
i.MakeNoise()
j.MakeNoise()
}
bark
meow
bark
meow
But it's super confusing because Go type cooerces a nil struct value to a non-nil (&type, nil) interface value. There's probably some naming or syntax way to make this clearer.
But the behavior is completely reasonable.
The underlying reason, which you hint on, is that in Go (unlike Python, Java, C#… even C++) the “type” of an “object” is not stored alongside the object.
A struct{a, b int32} takes 8 bytes of memory. It doesn't use any extra bytes to “know” its type, to point to a vtable of “methods,” to store a lock, or any other object “header.”
Dynamic dispatch in Go uses interfaces which are fat pointers that store the both type and a pointer to an object.
With this design it's only natural that you can have nil pointers, nil interfaces (no type and no pointer), and typed interfaces to a nil pointer.
This may be a bad design decision, it may be confusing. It's the reason why data races can corrupt memory.
But saying, as the author, “The reason for the difference boils down to again, not thinking, just typing” is just lazy.
Just as lazy as it is arguing Go is bad for portability.
I've written Go code that uses syscalls extensively and runs in two dozen different platforms, and found it far more sensible than the C approach.