Don't panic with 'omitempty' and uncomparable type

[arp242]

Fixes #360

[kkHAIKE]

i think use Value.IsZero is better..😊

[arp242]

i think use Value.IsZero is better..blush

You mean checking if the struct has the IsZero() bool method? I looked at that before in #353, and decided to go with this method. Is there any particular reason why you think IsZero() is better?

[kkHAIKE]

reflect.Value.IsZero() can use check struct fields all zero value.
https://github.com/golang/go/blob/f32519e5fbcf1b12f9654a6175e5e72b09ae8f3a/src/reflect/value.go#L1592-L1598

than not need use Comparable() to check..

[arp242]

I had to go back and look why I didn't use it @kkHAIKE, but the problem is that it considers e.g. []string{} to be non-zero, whereas we want to check the length.

Example program:

package main

import (
	"fmt"
	"reflect"
)

func main() {
	type Strukt struct{ Slice []int }

	a := reflect.ValueOf(Strukt{Slice: []int{1}})
	b := reflect.ValueOf(Strukt{Slice: []int{}})
	c := reflect.ValueOf(Strukt{})

	fmt.Printf("%-10s %-8s %s\n", "", "isZero", "isEmpty")
	fmt.Printf("%-10s %-8v %v\n", "values", a.IsZero(), isEmpty(a))
	fmt.Printf("%-10s %-8v %v\n", "[]int{}", b.IsZero(), isEmpty(b))
	fmt.Printf("%-10s %-8v %v\n", "no value", c.IsZero(), isEmpty(c))

}

func isEmpty(rv reflect.Value) bool {
	switch rv.Kind() {
	case reflect.Array, reflect.Slice, reflect.Map, reflect.String:
		return rv.Len() == 0
	case reflect.Struct:
		if rv.Type().Comparable() {
			return reflect.Zero(rv.Type()).Interface() == rv.Interface()
		}
		// Not comparable; need to loop over all fields and call isEmpty()
		// recursively so that we check the length for slices etc.
		for i := 0; i < rv.NumField(); i++ {
			if isEmpty(rv.Field(i)) {
				return true
			}
		}
	case reflect.Bool:
		return !rv.Bool()
	}
	return false
}

Outputs:

           isZero   isEmpty
values     false    false
[]int{}    false    true
no value   true     true

[kkHAIKE]

oh.. sorry, i forgot this case...change the impl to that

i think Array always not be length 0

func isEmpty(rv reflect.Value) bool {
	switch rv.Kind() {
	case Array:
		for i := 0; i < v.Len(); i++ {
			if !isEmpty(rv.Index(i)) {
				return false
			}
		}
		return true
	case reflect.Slice, reflect.Map:
		return rv.Len() == 0
	case reflect.Struct:
		for i := 0; i < rv.NumField(); i++ {
			if !isEmpty(rv.Field(i)) {
				return false
			}
		}
		return true
	}
	return rv.IsZero()
}

[arp242]

Cheers, thanks; I mentioned the discussion in #360; might be a few weeks before I look at this, but happy to accept PRs as long as they add decent test cases!