Even after practicing Golang for years, I can be surprised by some elementary features.
Today, I fixed a bug by taking cognizance of two peculiarities of Golang. Let me tell you.

If you don’t work with special characters, that may not interest you.

That first gotcha is very simple.
The builtin “len” applied on a string returns… the number of bytes. And not the number of letters.

func main() {
	a := "aééé"
	b := []rune(a)
	fmt.Println(len(a))
	fmt.Println(len(b))
}

You got…

7
4

https://play.golang.org/p/xs4XC8DkV4

I must confess… that was in the specifications.
https://golang.org/ref/spec#String_types

The kind of detail you can forget easily !

I took the habit to check the emptiness of a slice by comparing it to nil
It’s a gotcha. Look at this.

func main() {
 
	a := []int{1, 2, 3}
	var b []int
	a = a[:0] // Manual clean
 
	fmt.Println(a)
	fmt.Println(b)
 
	if a == nil {
		fmt.Println("a is nil")
	} else {
		fmt.Println("a is not nil")
	}
	if b == nil {
		fmt.Println("b is nil")
	} else {
		fmt.Println("b is not nil")
	}
}

And you got…

[]
[]
a is not nil
b is nil

https://play.golang.org/p/U7YpfI1mDA

Checking == nil is somewhat easier to write, but also insufficient to test emptiness of the slice.

Was it told in the specifications ?
Somewhat. Not clearly.
https://golang.org/ref/spec#Slice_types

That kind of detail can be a big loss of time.

I hope you may have gained some precious moments of debugging!

Thomas Solignac

Entrepreneur – Cofounder at Golem.ai (Paris, France)

I enjoy sharing Golang interesting patterns, experiments and tips.

http://golem.ai/