Why is this?

[Josh Kamau]

package main

import (
"fmt"
)

func main() {

fmt.Println(isInputNil(nil)) //Returns true
fmt.Println(isMapNil(nil)) //Returns false
}

func isMapNil(m map[string]interface{}) bool {
return isInputNil(m)
}

func isInputNil(input interface{}) bool {
return input == nil
}

https://play.golang.org/p/bBSFSdnOOk4

[Brian Candler]

You can think of an interface variable as a hidden struct: in pseudo-C, something like

struct {

    void *data;

    type_info *type;

}

If you assign a map to this (even a nil map), it still has a concrete type.  "data" is nil, but "type" is "map[X]Y"

Therefore the interface variable itself is not nil, as it now holds type info.

Maybe this helps:

https://play.golang.org/p/tmLu1ECc9s-

[Brian Candler]

Slightly extended:

https://play.golang.org/p/dVhNGS0oxKV

[Josh Kamau]

Thanks Brian, That makes sense.  

Josh

On Sat, 11 Apr 2020 at 17:26, Brian Candler <b.ca...@pobox.com> wrote:

Slightly extended:

https://play.golang.org/p/dVhNGS0oxKV

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