Assuming only arrays are passed as arguments to the arr parameter, I would like each call of unpackArray() to return the argument casted from its original array type to type []any.
package main
func unpackArray(arr any) []any {
return arr.([]any)
}
func main() {
myArr1 := []string {"Hey"}
myArr2 := []int {60}
unpackArray(myArr1)
unpackArray(myArr2)
}
However, this code yields error panic: interface conversion: interface {} is []string, not []interface {}. So it is not allowing me to cast an interface whose static type is not type []any to type []any.
So, given I know that arr's static type is some type of array, and without changing the arr parameter's initialization type from any, how could I convert arr to type []any using this function?
(I am encountering the same problem with maps where I cannot cast from an arbitrary map type to type map[any]any, but I am guessing the solution to this issue would be similar to the solution for arrays.)
Go does not have a builtin "cast" like this, but you can write a function to do it.
You may use reflection to convert a slice of any type to []any:
func unpackArray(s any) []any {
v := reflect.ValueOf(s)
r := make([]any, v.Len())
for i := 0; i < v.Len(); i++ {
r[i] = v.Index(i).Interface()
}
return r
}
You can also use generics in Go 1.18 or later:
func unpackArray[S ~[]E, E any](s S) []any {
r := make([]any, len(s))
for i, e := range s {
r[i] = e
}
return r
}
Both versions of these functions work as requested in the question:
myArr1 := []string {"Hey"}
myArr2 := []int {60}
unpackArray(myArr1)
unpackArray(myArr2)
Notes:
arr.([]any) is a type assertion. The expression asserts that the concrete value in the interface arr has type []any. The expression does not do any conversion.