Check empty struct that have array fields

Question

I have a nested (not embedded) struct for which some of field types are arrays.

How can I check if an instance of this struct is empty? (not using iteration!!)

Note that there can't use StructIns == (Struct{}) or by an empty instance! This code have this error:

invalid operation: user == model.User literal (struct containing model.Configs cannot be compared)

user.Configs.TspConfigs:

type TspConfigs struct {
    Flights     []Flights   `form:"flights" json:"flights"`
    Tours       []Tours     `form:"tours" json:"tours"`
    Insurances  []Insurances`form:"insurances" json:"insurances"`
    Hotels      []Hotels    `form:"hotels" json:"hotels"`
}

Iteration is the only possibility.

Jonathan Hall
– Jonathan Hall

2017-08-16 08:27:49 +00:00
Commented Aug 16, 2017 at 8:27 — Jonathan Hall
– Jonathan Hall, Commented Aug 16, 2017 at 8:27

icza · Accepted Answer · 2017-08-16 06:07:36Z

3

Those are slices, not arrays. It's important to emphasize as arrays are comparable but slices are not. See Spec: Comparision operators. And since slices are not comparable, structs composed of them (structs with fields having slice types) are also not comparable.

You may use reflect.DeepEqual() for this. Example:

type Foo struct {
    A []int
    B []string
}

f := Foo{}
fmt.Println("Zero:", reflect.DeepEqual(f, Foo{}))
f.A = []int{1}
fmt.Println("Zero:", reflect.DeepEqual(f, Foo{}))

Output (try it on the Go Playground):

Zero: true
Zero: false

answered Aug 16, 2017 at 6:07

icza

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1 Comment

Doug Henderson Over a year ago

I have used a package from github called deep or Deep which has a method similar to reflect.DeepEqual(), which also identifies the first non-equal component.

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