A sentinel error is a package-level variable used as a fixed, recognizable error value.

Example:

var ErrNotFound = errors.New("not found")

• Let callers check for a specific error using equality (`err == ErrNotFound`)

or (preferably) `errors.Is(err, ErrNotFound)` when wrapping is involved.

package store
 
import "errors"
 
var ErrNotFound = errors.New("not found")

• Sentinel errors are simple but can be too generic for large systems.
• Prefer typed errors when you need extra context (resource/id).
• If you wrap errors, use `errors.Is` to match the sentinel.

• sentinel /ˈsentɪnəl/: dấu hiệu nhận diện/cột mốc
• recognizable /ˈrekəɡnaɪzəbəl/: dễ nhận ra
• generic /dʒəˈnerɪk/: chung chung