golang cannot assign interface {} for struct

February 18, 2022

Hello Expert I’m using this libraray to store K/V in cache

"github.com/bluele/gcache"

The value which I store is this Data Structure

type LatestBlockhashCacheResult struct {
    Blockhash            string `json:"blockhash"`
    LastValidBlockHeight uint64 `json:"lastValidBlockHeight"` // Slot.
    CommitmentType  string `json:"commitmentType"`
}

lbhr := LatestBlockhashCacheResult{
            Blockhash:            lbh.Value.Blockhash.String(),
            LastValidBlockHeight: lbh.Value.LastValidBlockHeight,
            CommitmentType:       string(commitmentType),
        }
        gc.SetWithExpire(lbh.Value.LastValidBlockHeight, lbhr, time.Hour*10)

I have no problem with retrieving the cache but not able to Typecast it

c, _ := gc.Get(rf.LastValidBlockHeight)
    fmt.Printf("%T\n", c)

So when i Try this

var c = LatestBlockhashCacheResult{}
    c, _ = gc.Get(rf.LastValidBlockHeight)

This throws me error

cannot assign interface {} to c (type LatestBlockhashCacheResult) in multiple assignment: need type assertion

>Solution :

You are trying to assign interface{} to a typed variable.
In order to do this you need first try to cast the interface{} value to a specific type

val, err := gc.Get(rf.LastValidBlockHeight)
if err != nil {
  // handle 
}

c, ok := val.(LatestBlockhashCacheResult)
if !ok {
   // val has different type than LatestBlockhashCacheResult
}

Refs:
https://go.dev/tour/methods/15
https://go.dev/tour/methods/16