goNull / UndefinedMedium

Custom error type returning non-nil error on nil interface

Time: 0:00

BugFind the bug and fix the code

What it should do

Process a payment given a payment gateway interface. Example: processPayment(gateway) -> error

What happens instead

Error: gateway.Process is nil

package main

type PaymentGateway interface {
    Process(amount float64) error
}

type NullGateway struct {}

func (g NullGateway) Process(amount float64) error {
    return nil
}

type CustomError struct {}

func (e CustomError) Error() string {
    return "Custom error"
}

func processPayment(gateway PaymentGateway, amount float64) error {
    if gateway == nil {
        return CustomError{}
    }
    return gateway.Process(amount)
}

func main() {
    var gateway PaymentGateway
    _ = processPayment(gateway, 100.0)
}

Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).

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This bug belongs to the null and undefined errors pattern

Cannot read properties of undefined, NoneType has no attribute, NaN appearing from nowhere.

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package main type PaymentGateway interface { Process(amount float64) error } type NullGateway struct {} func (g NullGateway) Process(amount float64) error { return nil } type CustomError struct {} func (e CustomError) Error() string { return "Custom error" } func processPayment(gateway PaymentGateway, amount float64) error { if gateway == nil { return CustomError{} } return gateway.Process(amount) } func main() { var gateway PaymentGateway _ = processPayment(gateway, 100.0) }

Custom error type returning non-nil error on nil interface

What it should do

What happens instead

More null and undefined errors to practise

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Custom error type returning non-nil error on nil interface

What it should do

What happens instead

More null and undefined errors to practise

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