Ошибка	Последствие
Считать множественный возврат кортежем, который можно присвоить одной переменной	Это N отдельных значений: `v, err := f()` — на каждое нужна своя переменная (или `_`)
Игнорировать второе возвращаемое значение `err`	Ошибка молча теряется — корень большинства багов в Go-коде
Думать, что именованный результат надо инициализировать вручную	Он предобъявлен и уже обнулён (`0`, `""`, `nil`); голый `return` отдаст текущее значение
Злоупотреблять голым `return` в длинной функции	Неочевидно, что именно вернулось — на ревью это считают анти-паттерном
Передавать слайс в вариативную функцию без `...`	`f(s)` трактует слайс как один аргумент — нужно `f(s...)` для раскрытия
Ставить вариативный параметр не последним	Ошибка компиляции — `...T` обязан быть последним в списке параметров
Забыть базовый случай в рекурсии	Бесконечный самовызов растит стек горутины до `stack overflow` и паники
Рассчитывать на хвостовую оптимизацию, как в функциональных языках	Go её не гарантирует — глубокая рекурсия съедает стек; для горячих циклов берут итерацию

beginner

Functions

Functions in Go — multiple and named returns, the `return value, err` idiom, variadic parameters, first-class function values, anonymous functions, and recursion with a mandatory base case.

go-functions

Practice: 5 questions →

Sections

Contents

Detailed explanation

Functions

A function in Go is declared with func, and at first glance there is nothing to dig into: a name, parentheses with parameters, a return type, a body. But the function is the core unit of code, and it hosts a few idioms you cannot read real Go without: a function returns several values at once, and the value, err pair is the scaffold of all error handling; the ...int ellipsis parameter takes any number of arguments; the function itself is a value you can put in a variable and pass along.

Under the simple func sits the model interviews actually probe: multiple return is not a tuple but several separate values; named results are pre-declared and zeroed; a variadic parameter is an ordinary slice inside; a first-class function passes as an argument; and recursion grows the goroutine stack because Go guarantees no tail-call optimization. This topic walks functions layer by layer — from returns to recursion.

Topic map

Multiple & Named Returns — func f() (int, error) returns several values; the return value, err idiom; named results (n int, err error) are pre-declared and zeroed, and a naked return ships them — but don't lean on it.
Variadic Functions — func f(xs ...int): inside, xs is an ordinary []int; call it with a set of arguments or "spread" an existing slice via f(s...); the variadic parameter is always last.
Functions as Values — first-class functions: assign them to variables, pass them as arguments, return them from functions; the function type func(int) int; anonymous functions and the immediately-invoked func(){…}().
Recursion — a function calling itself; the mandatory base case; Go guarantees no tail-call optimization, so deep recursion grows the goroutine stack — for hot deep loops iteration is preferable.

Common mistakes and traps

Mistake	Consequence
Treating multiple return as a tuple you can assign to one variable	It is N separate values: `v, err := f()` — each needs its own variable (or `_`)
Ignoring the second return value `err`	The error is silently dropped — the root of most bugs in Go code
Thinking a named result must be initialised by hand	It is pre-declared and already zeroed (`0`, `""`, `nil`); a naked `return` ships its current value
Overusing a naked `return` in a long function	It is unclear what was actually returned — reviewers treat it as an anti-pattern
Passing a slice into a variadic function without `...`	`f(s)` treats the slice as one argument — you need `f(s...)` to spread it
Putting the variadic parameter anywhere but last	Compile error — `...T` must be the last parameter in the list
Forgetting the base case in recursion	Endless self-calls grow the goroutine stack to a `stack overflow` panic
Counting on tail-call optimization like in functional languages	Go does not guarantee it — deep recursion eats the stack; for hot loops use iteration

Why it matters for interviews

Functions are a common junior block: the question is never "how do you declare a func" but whether you grasp the idioms behind it. A candidate who copied code from examples but never studied the model stumbles right here.

What interviewers usually check:

How multiple return works and why the value, err pair is the basis of error handling.
What named results are, why they are convenient, and why a naked return should not be overused.
That a variadic parameter ...T is a slice inside, and how to "spread" an existing slice via s....
That functions in Go are first-class values: you can assign, pass, and return them.
Why deep recursion in Go is dangerous (no guaranteed tail-call optimization, the stack grows) and when to use iteration instead.

Why it matters

A function is the core unit of code in Go, and its small details separate a beginner from someone who understands the model. Multiple return is not a syntax trick but the scaffold of all error handling (`value, err`); a variadic parameter turns out to be an ordinary slice inside; a function sits happily in a variable and passes as an argument; and recursion grows the goroutine stack because the language guarantees no tail-call optimization. These are junior questions that trip up people who learned `func` but not what stands behind it.

Ошибка	Последствие
Считать множественный возврат кортежем, который можно присвоить одной переменной	Это N отдельных значений: `v, err := f()` — на каждое нужна своя переменная (или `_`)
Игнорировать второе возвращаемое значение `err`	Ошибка молча теряется — корень большинства багов в Go-коде
Думать, что именованный результат надо инициализировать вручную	Он предобъявлен и уже обнулён (`0`, `""`, `nil`); голый `return` отдаст текущее значение
Злоупотреблять голым `return` в длинной функции	Неочевидно, что именно вернулось — на ревью это считают анти-паттерном
Передавать слайс в вариативную функцию без `...`	`f(s)` трактует слайс как один аргумент — нужно `f(s...)` для раскрытия
Ставить вариативный параметр не последним	Ошибка компиляции — `...T` обязан быть последним в списке параметров
Забыть базовый случай в рекурсии	Бесконечный самовызов растит стек горутины до `stack overflow` и паники
Рассчитывать на хвостовую оптимизацию, как в функциональных языках	Go её не гарантирует — глубокая рекурсия съедает стек; для горячих циклов берут итерацию

beginner

Functions

Functions in Go — multiple and named returns, the `return value, err` idiom, variadic parameters, first-class function values, anonymous functions, and recursion with a mandatory base case.

go-functions

Practice: 5 questions →

Sections

Contents

Detailed explanation

Functions

Topic map

Multiple & Named Returns — func f() (int, error) returns several values; the return value, err idiom; named results (n int, err error) are pre-declared and zeroed, and a naked return ships them — but don't lean on it.
Variadic Functions — func f(xs ...int): inside, xs is an ordinary []int; call it with a set of arguments or "spread" an existing slice via f(s...); the variadic parameter is always last.
Functions as Values — first-class functions: assign them to variables, pass them as arguments, return them from functions; the function type func(int) int; anonymous functions and the immediately-invoked func(){…}().
Recursion — a function calling itself; the mandatory base case; Go guarantees no tail-call optimization, so deep recursion grows the goroutine stack — for hot deep loops iteration is preferable.

Common mistakes and traps

Mistake	Consequence
Treating multiple return as a tuple you can assign to one variable	It is N separate values: `v, err := f()` — each needs its own variable (or `_`)
Ignoring the second return value `err`	The error is silently dropped — the root of most bugs in Go code
Thinking a named result must be initialised by hand	It is pre-declared and already zeroed (`0`, `""`, `nil`); a naked `return` ships its current value
Overusing a naked `return` in a long function	It is unclear what was actually returned — reviewers treat it as an anti-pattern
Passing a slice into a variadic function without `...`	`f(s)` treats the slice as one argument — you need `f(s...)` to spread it
Putting the variadic parameter anywhere but last	Compile error — `...T` must be the last parameter in the list
Forgetting the base case in recursion	Endless self-calls grow the goroutine stack to a `stack overflow` panic
Counting on tail-call optimization like in functional languages	Go does not guarantee it — deep recursion eats the stack; for hot loops use iteration

Why it matters for interviews

What interviewers usually check:

How multiple return works and why the value, err pair is the basis of error handling.
What named results are, why they are convenient, and why a naked return should not be overused.
That a variadic parameter ...T is a slice inside, and how to "spread" an existing slice via s....
That functions in Go are first-class values: you can assign, pass, and return them.
Why deep recursion in Go is dangerous (no guaranteed tail-call optimization, the stack grows) and when to use iteration instead.

Why it matters

Функции

Функции

Карта темы

Частые ошибки и ловушки

Значение для собеседований

Functions

Functions

Topic map

Common mistakes and traps

Why it matters for interviews

Функции

Функции

Карта темы

Частые ошибки и ловушки

Значение для собеседований

Functions

Functions

Topic map

Common mistakes and traps

Why it matters for interviews