Function Signatures
Fast recall
Quick revision
Core answer
Whether you understand Function Signatures beyond memorized syntax.
Giving a definition without explaining a practical trade-off.
Connect the concept to a small production example and state its complexity or failure mode.
Interview-ready guide
Interview answer
The anatomy:
func divide(a, b int) (int, error)
// func keyword
// divide name (not part of the type)
// a, b parameter names (docs only — not the type)
// int the shared parameter type
// (int, error) the resultsThe signature AS A TYPE — what matters for assigning functions to variables, passing them, comparing:
type MathFunc func(int, int) int
add := func(a, b int) int { return a + b }
var m MathFunc = add // fits the signature type
m(3, 4) // 7 — executedfunc(int, int) int IS a type — a function type. Variable names in signatures are documentation (godoc shows them, callers read them), but two functions with the same types and different names are the SAME type.
The signature variants: single result can drop the parens (func f() int); multiple results need them (func f() (int, error)); zero results (func f()); variadic (func f(nums ...int) — the last parameter); named results (func f() (result int, err error) — zero-initialized, naked-returnable, defer-mutable).
The comparison boundary: function types are comparable only to nil (func values compare false against nil, anything else is a compile error). They're not equatable values — two identical functions aren't == comparable (you compare by calling or by identity through pointers if you must).
Function Signatures
Direct Answer
func name(params) results — the parameter list (names optional, types required), and the result list (optional, can be named). Types are what matter for identity: func(int, string) error is the signature — parameter NAMES are documentation, not part of the type.
Deep Dive & Architecture
Why signatures matter architecturally: interfaces are METHOD SIGNATURES (the methods topic) — the whole implicit-satisfaction system is signature matching. Accepting func types in APIs (http.HandlerFunc is a signature-shaped type) gives Go its middleware pattern. The signature is the contract; the body is an implementation detail.
Common Mistakes & Pitfalls
Giving a definition without explaining a practical trade-off.
Check your understanding
Answer these without looking back at the article.
- When would you use Function Signatures in a real project?
- How would you compare Function Signatures with an alternative?
- What is a common mistake when using Function Signatures?
Looking for a structured roadmap?
Every module on this page is also part of the full Java backend interview track.