How to create a custom error type by embedding the error interface in Go?

To create a custom error type by embedding the error interface in Go, follow these steps:

Define a new struct type that will represent your custom error type. This struct should embed the error interface.

type CustomError struct {
    message string
}

Implement the Error() method for your custom error type. This method should return the error message.

func (e CustomError) Error() string {
    return e.message
}

Create a constructor function that initializes and returns an instance of your custom error type.

func NewCustomError(message string) CustomError {
    return CustomError{message}
}

Use your custom error type in your code by creating an instance of it using the constructor function.

func DoSomething() error {
    // ...
    if somethingWentWrong {
        return NewCustomError("Something went wrong")
    }
    // ...
}

To handle the custom error type, you can use a type assertion to check if the returned error is of your custom type.

err := DoSomething()
if customErr, ok := err.(CustomError); ok {
    // Handle the custom error
    fmt.Println(customErr.message)
} else {
    // Handle other types of errors
    fmt.Println(err)
}

By embedding the error interface and implementing the Error() method, you can create a custom error type with your own error message.