这是一个空值struct nil

Question

Look at the following code snippet.

package main

import "fmt"

type Empty struct {
    Field1, Field2 string
}

func main() {

    value := Empty{}

    fmt.Println(value == nil)
    fmt.Printf("%p", &value)

}

I've got compiler error

./empty_struct.go:19: cannot convert nil to type Empty

How can I check a value struct type, if it is empty or not?

Answer 1

Pointers, slices, channels, interfaces and maps are the only types that can be compared to nil. A struct value cannot be compared to nil.

If all fields in the struct are comparable (as they are in your example), then you can compare with a known zero value of the struct:

 fmt.Println(value == Empty{})

If the struct contains fields that are not comparable (slices, maps, channels), then you need to write code to check each field:

 func IsAllZero(v someStructType) bool {
     return v.intField == 0 && v.stringField == "" && v.sliceField == nil
 }
 ...
 fmt.Println(isAllZero(value))