golang append() evaluated but not used
ArraysGoVarArrays Problem Overview
func main(){
var array [10]int
sliceA := array[0:5]
append(sliceA, 4)
fmt.Println(sliceA)
}
> Error : append(sliceA, 4) evaluated but not used
I don't Know why? The slice append operation is not run...
Arrays Solutions
Solution 1 - Arrays
Refer: Appending to and copying slices
In Go, arguments are passed by value.
Typical append
usage is:
a = append(a, x)
You need to write:
func main(){
var array [10]int
sliceA := array[0:5]
// append(sliceA, 4) // discard
sliceA = append(sliceA, 4) // keep
fmt.Println(sliceA)
}
Output:
[0 0 0 0 0 4]
I hope it helps.
Solution 2 - Arrays
sliceA = append(sliceA, 4)
append()
returns a slice containing one or more new values.
Note that we need to accept a return value from append as we may get a new slice value.
Solution 3 - Arrays
you may try this:
sliceA = append(sliceA, 4)
built-in function append([]type, ...type)
returns an array/slice of type, which should be assigned to the value you wanted, while the input array/slice is just a source. Simply, outputSlice = append(sourceSlice, appendedValue)
Solution 4 - Arrays
Per the Go docs:
> The resulting value of append is a slice containing all the elements of the original slice plus the provided values.
So the return value of 'append', will contain your original slice with the appended portion.
Solution 5 - Arrays
The key to understand is that slice is just a "view" of the underling array. You pass that view to the append function by value, the underling array gets modified, at the end the return value of append function gives you the different view of the underling array. i.e. the slice has more items in it
your code
sliceA := array[0:5] // sliceA is pointing to [0,5)
append(sliceA, 4) // sliceA is still the original view [0,5) until you do the following
sliceA = append(sliceA, 4)
reference: https://blog.golang.org/slices