How do I create an array of int arrays in Golang using slice literals?
I've tried
test := [][]int{[1,2,3],[1,2,3]}
and
type Test struct {
foo [][]int
}
bar := Test{foo: [[1,2,3], [1,2,3]]}
4 Answers
You almost have the right thing however your syntax for the inner arrays is slightly off, needing curly braces like; test := [][]int{[]int{1,2,3},[]int{1,2,3}} or a slightly more concise version; test := [][]int{{1,2,3},{1,2,3}}
The expression is called a 'composite literal' and you can read more about them here; https://golang.org/ref/spec#Composite_literals
But as a basic rule of thumb, if you have nested structures, you have to use the syntax recursively. It's very verbose.
4 Comments
twotwotwo
You don't have to use the same syntax for the inner arrays: play.golang.org/p/Wdhabb3qca
evanmcdonnal
@twotwotwo true, that is technically different and imo preferred.
twotwotwo
Glad you added the shorter example, but the answer still says "you have to use the syntax recursively. It's very verbose," and "you have to use the same syntax for the inner arrays," which seem confusing or inaccurate when you consider that inner slices can be written out in a different and shorter way.
evanmcdonnal
@twotwotwo alright well I've changed my wording. I think that's nitpicking. It is the same syntax, they're both covered as 'composite literal' it's just in the case of the inner collections the type information can be inferred but using
[] vs {} is really the important distinction.In some other langauges (Perl, Python, JavaScript), [1,2,3] might be an array literal, but in Go, composite literals use braces, and here, you have to specify the type of the outer slice:
package main
import "fmt"
type T struct{ foo [][]int }
func main() {
a := [][]int{{1, 2, 3}, {4, 5, 6}}
b := T{foo: [][]int{{1, 2, 3}, {4, 5, 6}}}
fmt.Println(a, b)
}
You can run or play with that on the Playground.
The Go compiler is just tricky enough to figure out that the elements of an [][]int are []int without you saying so on each element. You do have to write out the outer type's name, though.
Comments
Just replace the square brackets with curly braces. In Go, array literals are identified with curly braces.
test := [][]int{{1,2,3},{1,2,3}}
Comments
A slice literal is written as []type{<value 1>, <value 2>, ... }. A slice of ints would be []int{1,2,3} and a slice of int slices would be [][]int{[]int{1,2,3},[]int{4,5,6}}.
groups := [][]int{[]int{1,2,3},[]int{4,5,6}}
for _, group := range groups {
sum := 0
for _, num := range group {
sum += num
}
fmt.Printf("The array %+v has a sum of %d\n", sub, sum)
}
1 Comment
twotwotwo
You don't have to specify the types of the values: play.golang.org/p/Wdhabb3qca
[N]type{42, 33, 567}or[...]type{42, 33, 567}— to get the size inferred from the number of member in the initializer.