Errors

Return error values

The error interface is the standard failure signal. nil means success.

import (
	"errors"
	"fmt"
)

func find(id int) (string, error) {
	if id <= 0 {
		return "", errors.New("id must be positive")
	}
	return "ok", nil
}

Check errors immediately

Handle the error before using the result.

name, err := find(0)
if err != nil {
	fmt.Println("error:", err)
	return
}
fmt.Println(name)

Wrap context

fmt.Errorf with %w wraps an error for later inspection.

return "", fmt.Errorf("find user: %w", err)

Error habits

• Do not ignore errors with a blank identifier casually
• Add context when returning errors up the stack
• Compare sentinel errors with errors.Is
• Panic is for truly unexpected failures, not normal control flow