Cannot Embed Unexported Interface

Why This Happens

In Go, you can only embed exported types from other packages. If the interface or struct type starts with a lowercase letter, it is unexported and cannot be embedded from outside its package.

The Problem

// package auth
type validator interface {
    Validate() error
}

// package main
type MyAuth struct {
    auth.validator // cannot embed unexported type
}

The Fix

// package auth
type Validator interface {
    Validate() error
}

// package main
type MyAuth struct {
    auth.Validator
}

Step-by-Step Fix

1. 1

   Identify the unexported type

   Check if the embedded type starts with a lowercase letter.

2. 2

   Export the type

   Capitalize the first letter of the type name in the defining package.

3. 3

   Update all references

   Update all references to the type to use the new capitalized name.