JuniorTheoryCommon

What does the program print?

package main

import "errors"
import "fmt"

type NotFound struct{ ID int }

func (e *NotFound) Error() string { return "not found" }
func main() {
    var nf *NotFound
    fmt.Println(errors.As(fmt.Errorf("load: %w", &NotFound{ID: 7}), &nf))
}

true

Expecting false: errors.As walks the whole chain that %w builds, so it finds the *NotFound inside the wrapper and stores it in nf.
Expecting &nf not to compile: errors.As takes the address of a variable of the type it looks for, here a pointer to a *NotFound variable.

What would errors.Is(err, &NotFound{ID: 7}) return for the same wrapped error, and why?
What happens if you pass nf instead of &nf to errors.As?

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JuniorTheoryCommon

What does the program print?

package main

import "errors"
import "fmt"

type NotFound struct{ ID int }

func (e *NotFound) Error() string { return "not found" }
func main() {
    var nf *NotFound
    fmt.Println(errors.As(fmt.Errorf("load: %w", &NotFound{ID: 7}), &nf))
}

true

Expecting false: errors.As walks the whole chain that %w builds, so it finds the *NotFound inside the wrapper and stores it in nf.
Expecting &nf not to compile: errors.As takes the address of a variable of the type it looks for, here a pointer to a *NotFound variable.

What would errors.Is(err, &NotFound{ID: 7}) return for the same wrapped error, and why?
What happens if you pass nf instead of &nf to errors.As?

Back to questions Open topic in roadmap →Answer it yourself — Quiz