I'm having troubles with:

• *map[...]...
• Struct
• []Struct

I still think these should not be allowed, but instead use:

• map[...]...
• *Struct
• []*Struct

But maybe I'm just not getting the whole thing?

cc: @stevehipwell - @alexandear - @zyfy29 - please help me make sense of how we should handle omitzero in this repo, as I'm really struggling with this one.

Should I go ahead with this :

Allowing only - map[...]... , *Struct , []*Struct and []buildin as suggested.

I tried a few small experiments with different field shapes. From what I observed, even when the data is “empty”, these values are still considered non-zero and therefore are not omitted during marshaling.

I tested with the following example.

type DummyDataForOmitZero struct {
	OmitZeroWithoutPointerSlice []int  `json:"omit_zero_without_pointer_slice,omitzero"`
	OmitZeroWithPointerSlice    []*int `json:"omit_zero_with_pointer_slice,omitzero"`

	OmitZeroWithoutPointerStruct Struct  `json:"omit_zero_without_pointer_struct,omitzero"`
	OmitZeroWithPointerStruct    *Struct `json:"omit_zero_with_pointer_struct,omitzero"`

	OmitZeroWithoutPointerSliceofStruct []Struct  `json:"omit_zero_without_pointer_sliceofstruct,omitzero"`
	OmitZeroWithPointerSliceofStruct    []*Struct `json:"omit_zero_with_pointer_sliceofstruct,omitzero"`

	OmitZeroWithoutPointerMap map[string]string  `json:"omit_zero_without_pointer_map,omitzero"`
	OmitZeroWithPointerMap    *map[string]string `json:"omit_zero_with_pointer_map,omitzero"`
}

Empty input:

		data := DummyDataForOmitZero{
			OmitZeroWithoutPointerSlice:         []int{},
			OmitZeroWithPointerSlice:            []*int{},
			OmitZeroWithoutPointerSliceofStruct: []Struct{},
			OmitZeroWithPointerSliceofStruct:    []*Struct{},
			OmitZeroWithoutPointerStruct:        Struct{},
			OmitZeroWithPointerStruct:           &Struct{},
			OmitZeroWithoutPointerMap:           map[string]string{},
			OmitZeroWithPointerMap:              &map[string]string{},
		}

Marshaled output:

{
  "omit_zero_without_pointer_slice": [],
  "omit_zero_with_pointer_slice": [],
  "omit_zero_with_pointer_struct": {},
  "omit_zero_without_pointer_sliceofstruct": [],
  "omit_zero_with_pointer_sliceofstruct": [],
  "omit_zero_without_pointer_map": {},
  "omit_zero_with_pointer_map": {}
}

or should non-pointer values be allowed as well?
any opinion?

Awesome... thank you for the excellent experiment... that is useful to see the results.

Here's my opinion, and I am totally happy to be corrected or discuss:

I have some ideas of what should never be used in this repo (regardless the JSON tags) unless there is a REALLY GOOD reason (which, granted, does indeed sometimes happen):

• pointers to slices or maps (which are already reference types)
• slices of pointers to primitives
• slices of structs without the pointers (for iteration)

As for the use of omitzero, I don't have a good enough "feel" for them yet to really understand their use.

Looking carefully at the above experiment, only one case was removed by omitzero:

• OmitZeroWithoutPointerStruct Struct json:"omit_zero_without_pointer_struct,omitzero"

But I'm struggling to figure out if that is a really useful case in this repo. It seems like a very targeted and specific use case... one that we might indeed find useful, but honestly I don't know where.

So in my opinion, if we still don't allow my list above, then I think we may be able to proceed.

make sense.
I’ll proceed with -

Allowing only

• map[...]...
• *Struct
• []*Struct
• []builtin (e.g. []int, []string .... )

We can adjust the linter later if necessary.