Ошибка	Последствие
Игнорировать возвращённую ошибку через `_`	Сбой проглатывается молча — `value, _ := strconv.Atoi(s)` спрячет невалидный ввод
Ставить `error` не последним возвращаемым значением	Нарушает идиому; читатель и линтер ждут `error` именно в конце
Ждать, что неудача «выбросится» сама, как исключение	В Go ошибка не всплывает — пока её явно не вернуть выше, её просто нет
Использовать `panic` для ожидаемой неудачи (нет файла, плохой ввод)	`panic` — только для исключительного; обычный сбой должен быть `error`
Возвращать «пустой» результат без проверки `err`	При `err != nil` результат не определён — читать его до проверки опасно
Путать `errors.New` и `fmt.Errorf`	`errors.New` — фиксированный текст; `fmt.Errorf` — форматирование и обёртывание через `%w`

beginner

Errors

An error in Go is an ordinary value: a function returns `(result, error)` as its last value, `nil` means success, and the caller checks `if err != nil` right after the call.

go-errors-basics

Practice: 4 questions →

Sections

Contents

Detailed explanation

Errors

Go has no exceptions for ordinary failures. When a function may not succeed — it cannot find a file, parse a number, or reach the network — it returns the error as an ordinary value: an error is the last item in the result list. The caller receives that value and decides what to do: handle it on the spot, return it upward, or — more rarely — ignore it deliberately. No try/catch, no automatic "bubbling" — the flow of execution stays explicit and linear.

Behind that simplicity sit a few decisions the junior section probes: error is an interface, an ordinary value you can return, store in a variable, and compare with nil; an error is created with errors.New or fmt.Errorf; and panic exists separately — only for genuinely exceptional situations, not for expected failures. This topic walks the basics of error handling layer by layer — from the return idiom to the canonical if err != nil check. The depth of wrapping (%w, errors.Is/errors.As, sentinel errors) is covered by the separate Error Handling topic.

Topic map

Returning Errors — the (result, error) idiom: the error is the last returned value; nil means success; the caller decides what to do next.
errors.New & fmt.Errorf — create an error from text with errors.New("text") or a formatted one with fmt.Errorf("...: %v", x); the %w verb wraps (deep wrapping lives in go-error-handling).
An Error Is a Value — error is a plain interface you return, store, and inspect; unlike panic, it is not an exception but part of a function's normal result.
The if err != nil Idiom — check the error immediately after the call and either handle it or return early; don't silence it with _; verbose but explicit control flow.

Common mistakes and traps

Mistake	Consequence
Ignoring the returned error with `_`	The failure is swallowed silently — `value, _ := strconv.Atoi(s)` hides invalid input
Putting `error` somewhere other than last among return values	Breaks the idiom; readers and linters expect `error` exactly at the end
Expecting a failure to "throw" itself, like an exception	In Go an error does not bubble up — until you explicitly return it upward, it is simply not there
Using `panic` for an expected failure (missing file, bad input)	`panic` is for the exceptional only; an ordinary failure must be an `error`
Returning a "blank" result without checking `err`	When `err != nil` the result is undefined — reading it before the check is dangerous
Confusing `errors.New` and `fmt.Errorf`	`errors.New` is fixed text; `fmt.Errorf` is formatting and wrapping via `%w`

Why it matters for interviews

Error handling is the junior-level filter for "understands Go's model" versus "carries habits over from languages with exceptions." The idiom itself is trivial, but the very difference from try/catch is asked almost every time.

What interviewers usually check:

How a Go function reports a failure and why error is the last returned value.
That error is an ordinary value (an interface), not a thrown exception, and who decides what to do with it.
How errors.New differs from fmt.Errorf and what the %w verb does.
Why a nil error means success and why the result must not be read before checking err.
How panic/recover differs from ordinary error handling and when panic is appropriate (exceptional cases, not expected failures).

Why it matters

Error handling in Go is unfamiliar to anyone coming from languages with exceptions: there is no `try`/`catch` for ordinary failures — a function simply returns an `error` as its last value, and the caller is obliged to check it. The junior question catches exactly those who ignore the returned error with `_`, confuse `error` with `panic`, or expect a failure to "throw" itself. The `if err != nil` idiom is verbose, but that verbosity is what interviews ask about almost every time: why an error is a value, who decides what to do with it, and how `errors.New` differs from `fmt.Errorf`.

Ошибка	Последствие
Игнорировать возвращённую ошибку через `_`	Сбой проглатывается молча — `value, _ := strconv.Atoi(s)` спрячет невалидный ввод
Ставить `error` не последним возвращаемым значением	Нарушает идиому; читатель и линтер ждут `error` именно в конце
Ждать, что неудача «выбросится» сама, как исключение	В Go ошибка не всплывает — пока её явно не вернуть выше, её просто нет
Использовать `panic` для ожидаемой неудачи (нет файла, плохой ввод)	`panic` — только для исключительного; обычный сбой должен быть `error`
Возвращать «пустой» результат без проверки `err`	При `err != nil` результат не определён — читать его до проверки опасно
Путать `errors.New` и `fmt.Errorf`	`errors.New` — фиксированный текст; `fmt.Errorf` — форматирование и обёртывание через `%w`

beginner

Errors

An error in Go is an ordinary value: a function returns `(result, error)` as its last value, `nil` means success, and the caller checks `if err != nil` right after the call.

go-errors-basics

Practice: 4 questions →

Sections

Contents

Detailed explanation

Errors

Topic map

Returning Errors — the (result, error) idiom: the error is the last returned value; nil means success; the caller decides what to do next.
errors.New & fmt.Errorf — create an error from text with errors.New("text") or a formatted one with fmt.Errorf("...: %v", x); the %w verb wraps (deep wrapping lives in go-error-handling).
An Error Is a Value — error is a plain interface you return, store, and inspect; unlike panic, it is not an exception but part of a function's normal result.
The if err != nil Idiom — check the error immediately after the call and either handle it or return early; don't silence it with _; verbose but explicit control flow.

Common mistakes and traps

Mistake	Consequence
Ignoring the returned error with `_`	The failure is swallowed silently — `value, _ := strconv.Atoi(s)` hides invalid input
Putting `error` somewhere other than last among return values	Breaks the idiom; readers and linters expect `error` exactly at the end
Expecting a failure to "throw" itself, like an exception	In Go an error does not bubble up — until you explicitly return it upward, it is simply not there
Using `panic` for an expected failure (missing file, bad input)	`panic` is for the exceptional only; an ordinary failure must be an `error`
Returning a "blank" result without checking `err`	When `err != nil` the result is undefined — reading it before the check is dangerous
Confusing `errors.New` and `fmt.Errorf`	`errors.New` is fixed text; `fmt.Errorf` is formatting and wrapping via `%w`

Why it matters for interviews

What interviewers usually check:

How a Go function reports a failure and why error is the last returned value.
That error is an ordinary value (an interface), not a thrown exception, and who decides what to do with it.
How errors.New differs from fmt.Errorf and what the %w verb does.
Why a nil error means success and why the result must not be read before checking err.
How panic/recover differs from ordinary error handling and when panic is appropriate (exceptional cases, not expected failures).

Why it matters

Ошибки

Ошибки

Карта темы

Частые ошибки и ловушки

Значение для собеседований

Errors

Errors

Topic map

Common mistakes and traps

Why it matters for interviews

Ошибки

Ошибки

Карта темы

Частые ошибки и ловушки

Значение для собеседований

Errors

Errors

Topic map

Common mistakes and traps

Why it matters for interviews