Golang in sixty seconds — three dots…

The three-dot ... notation can be used in a few places:

To specify length when creating array literals

arr := [...]string{"One", "Two", "Three", "Four", "Five"}
fmt.Println(len(arr)) // 5

Note that this creates an array with a fixed length, not a slice. So methods like append this will not work.

Variadic Functions

This is a function that can take any number of trailing arguments. Create a variadic function by prefixing the type with ... like this:

func sum(nums ...int) int {
  total := 0
  for _, num := range nums {
    total += num
  }
  return total
}

In this example, nums will be a slice of ints. You would call sum like this:

total := sum(1, 2, 15, 24)
fmt.Println(total) // 42

You can also use the ... a notation to pass a slice (not an array) into a variadic function like this:

slice := []int{2, 5, 9, 8}
total = sum(slice...)
fmt.Println(total) // 24

Try it here

Wildcard for package lists

You’ll most likely have seen or used this command already:

go test ./...

It simply means “test all packages in this directory (and subdirectories)”

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