Parameters, multiple returns, variadic, closures, and defer.

Function Basics

Functions are declared with func, then the name, parameters, and return type.

func add(a int, b int) int {
    return a + b
}

If consecutive parameters share a type, you can write the type once:

func add(a, b int) int { return a + b }

Calling functions

Functions are values

In Go, functions are first-class values — you can pass them around like any other data.

Here double is an anonymous function assigned to a variable. func(int) int is the type of "a function that takes one int and returns one int".

No optional/default arguments

Go doesn't have default values for parameters or named arguments. The Go way is to provide additional functions or pass a struct:

// Awkward in some languages, normal in Go:
type ListOptions struct {
    Limit  int
    Cursor string
}

func List(opts ListOptions) ([]Item, error) { ... }

No overloading either

Two functions can't share a name with different signatures. The Go way is just to pick different names:

func PrintInt(x int)        { ... }
func PrintFloat(x float64)  { ... }
// — or use generics (Chapter 13).