mistake. Returns false if it contains slices

Question content

Error.Is doesn't seem to work properly when I have an error structure that contains slices nested within it:

package main

import (
    "errors"
    "fmt"
    "os"
)

type Response struct {
    Details []string
}

type ErrResponseError struct {
    Response Response
}

func (err ErrResponseError) Error() string {
    return "response error"
}

func main() {
    err := ErrResponseError{}
    fmt.Fprintf(os.Stdout, "equal: %v", errors.Is(err, ErrResponseError{}))
}

return

equal: false

package main

import (
    "errors"
    "fmt"
    "os"
)

type Response struct {
    Details string // Changed this line
}

type ErrResponseError struct {
    Response Response
}

func (err ErrResponseError) Error() string {
    return "response error"
}

func main() {
    err := ErrResponseError{}
    fmt.Fprintf(os.Stdout, "equal: %v", errors.Is(err, ErrResponseError{}))
}

return

equal: true

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Solution

From the documentation:

So you can do this by writing an Is method to compare the two slices.

The default error comparison algorithm checks whether the error is equal to the target. Since your error contains a slice, it's not comparable.

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