go-define-custom-error-struct.go

package main

import (
    "fmt"
    "github.com/pkg/errors"
)

// Custom Error Type
type InvalidInputError struct {
    Field   string
    Message string
}

// Implement the error interface
func (e *InvalidInputError) Error() string {
    return fmt.Sprintf("invalid input for field '%s': %s", e.Field, e.Message)
}

// Example Function
func calculateDiscount(price float64, discountPercent float64) (float64, error) {
    if price < 0 {
        return 0, errors.Wrap(&InvalidInputError{Field: "price", Message: "must be non-negative"}, "calculateDiscount failed")
    }
    if discountPercent < 0 || discountPercent > 100 {
        return 0, errors.Wrap(&InvalidInputError{Field: "discountPercent", Message: "must be between 0 and 100"}, "calculateDiscount failed")
    }

    discountAmount := price * discountPercent / 100
    return price - discountAmount, nil
}

func main() {
    discountedPrice, err := calculateDiscount(-10, 20)
    if err != nil {
        fmt.Printf("Error: %+v\n", err) // Print the error with stack trace
        if inputErr, ok := errors.Cause(err).(*InvalidInputError); ok {
            fmt.Println("Invalid input:", inputErr.Field, inputErr.Message) // Access specific error details
        }
        return
    }
    fmt.Println("Discounted price:", discountedPrice)
}