What is the difference between error and exception?

Question

Accepted Answer

**error** — a Go interface for expected failures (value-based). **Exception** — not a Go concept (Java/C++ use try-catch; Go uses panic/recover).

**The error interface:**
```go
type error interface {
    Error() string
}
```
Any type with `Error() string` method implements this interface.

**Error creation patterns:**
```go
// Sentinel errors
var ErrNotFound = errors.New("not found")

// Custom error types
type APIError struct {
    Code    int
    Message string
}

func (e *APIError) Error() string {
    return fmt.Sprintf("api error %d: %s", e.Code, e.Message)
}

// Wrapping errors
func fetch(url string) ([]byte, error) {
    resp, err := http.Get(url)
    if err != nil {
        return nil, fmt.Errorf("fetching %s: %w", url, err)
    }
    defer resp.Body.Close()
    return io.ReadAll(resp.Body)
}
```

**Error handling:**
```go
// errors.Is for sentinel errors
if errors.Is(err, ErrNotFound) {
    // handle
}

// errors.As for custom errors
var apiErr *APIError
if errors.As(err, &apiErr) {
    fmt.Println(apiErr.Code)
}
```

**Go philosophy:**
- "Errors are values."
- Explicit handling.
- Handle where they occur.

**Common mistakes:**
- Ignoring errors.
- Not wrapping errors.
- Using `==` instead of `errors.Is()`.
- Creating error strings with capitals.
- Overusing panic.

Go: What is the difference between error and exception?