Check if a value exists in map using an internal function from that struct

Question

I've this struct

type Zones map[uint64]Zone

And I want to have a method to find a value in that map, something like this.

func (z *Zones) findById(id uint64) (Zone, error) {
    if zone, ok := z[id]; ok {
        return zone, nil
    } else {
        return zone{}, errors.New(fmt.Sprintf("Zone %d not found", id))
    }
}

But in this line:

if zone, ok := z[id]; ok {

I'm getting this error:

Assignment count mismatch: 2=1.

Theres a lot of links which suggest that we can check if a value exists in a map with that line, I have no idea what is happening. What am I doing wrong?

Thanks in advance.

The error you should be getting is `invalid operation: z[id] (type *Zones does not support indexing)` — RayfenWindspear, Dec 11 '18 at 23:36

score 4 · Accepted Answer · answered Dec 11 '18 at 23:36

4

The type *Zone does not support indexing. It's a pointer, not a map. Dereference the pointer to fix the code:

func (z *Zones) findById(id uint64) (Zone, error) {
    if zone, ok := (*z)[id]; ok { // <-- note change on this line
        return zone, nil
    } else {
        return Zone{}, errors.New(fmt.Sprintf("Zone %d not found", id))
    }
}

answered Dec 11 '18 at 23:36

Charlie Tumahai

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Thank you very much! :) – Martin Dec 11 '18 at 23:37

Check if a value exists in map using an internal function from that struct

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