Array and slice data types

arrays go slice pass-by-value func
duganets picture duganets · Jul 31, 2012 · Viewed 30.3k times · Source

I found myself confused with the array and slice data types.

From Go docs, arrays are described as follows:

There are major differences between the ways arrays work in Go and C. In Go,

  • Arrays are values. Assigning one array to another copies all the elements.
  • In particular, if you pass an array to a function, it will receive a copy of the array, not a pointer to it.
  • The size of an array is part of its type. The types [10]int and [20]int are distinct.

Functions:

As in all languages in the C family, everything in Go is passed by value. That is, a function always gets a copy of the thing being passed, as if there were an assignment statement assigning the value to the parameter. For instance, passing an int value to a function makes a copy of the int, and passing a pointer value makes a copy of the pointer, but not the data it points to.

Why does sort.Ints(arrayValue) modify the passed variable when I declared it as an array, not as a slice?

Code

var av = []int{1,5,2,3,7}

fmt.Println(av)
sort.Ints(av)
fmt.Println(av)
return

Output

[1 5 2 3 7]
[1 2 3 5 7]

Answer

VonC picture VonC · Jul 31, 2012

See "Slices: usage and internals"

var av = []int{1,5,2,3,7}

That is a slice, not an array.

A slice literal is declared just like an array literal, except you leave out the element count.

That explains why the sort function will modify the content of what is referenced by the slice.

As commented below by Kirk, sort.Ints will give you an error if you passed it an array instead of a slice.

func Ints(a []int)

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