I have the following:
type Int32A int32
type Int32B int32
and would like to implement a function that can accept any slice of types whose kind is reflect.Int32
and convert it into []int32
. For example:
func ConvertTypeSliceToInt32Slice(es «es-type») []int32 {
result := make([]int32, len(es))
for i := 0; i < len(result); i {
result[i] = es[i].(int32)
}
return result
}
func caller() {
Int32as := Int32A{1, 2}
Int32bs := Int32B{3, 5}
int32as := ConvertTypeSliceToInt32Slice(Int32as)
int32bs := ConvertTypeSliceToInt32Slice(Int32bs)
}
How can this be done far any arbitrary type definition whose kind is reflect.Int32
? (Context: this function will be used to convert slices of proto
enum
s; ie the full set of types is unknown and unbounded so performing a switch
on each type isn't feasible).
Also, I'm using 1.17
so I can't use parameterized types (aka templates).
One attempt that doesn't work (it panics at is.([]interface{})
):
func ConvertTypeSliceToInt32Slice(is interface{}) []int32 {
es := is.([]interface{})
result := make([]int32, len(es))
for i := 0; i < len(result); i {
result[i] = es[i].(int32)
}
return result
}
CodePudding user response:
int32
in this case is an "underlying type", and ~
in a type parameter is how you specify a constraint to an underlying type.
For example: https://go.dev/play/p/8-WAu9KlXl5
func ConvertTypeSliceToInt32Slice[T ~int32](es []T) []int32 {
result := make([]int32, len(es))
for i := 0; i < len(result); i {
result[i] = int32(es[i])
}
return result
}
If you need to use reflection, you can convert the type of each element before appending to the final slice:
func ConvertTypeSliceToInt32Slice(es interface{}) []int32 {
v := reflect.ValueOf(es)
int32ty := reflect.TypeOf(int32(0))
result := make([]int32, v.Len())
for i := 0; i < v.Len(); i {
result[i] = v.Index(i).Convert(int32ty).Interface().(int32)
}
return result
}
And if you need to ensure other convertible numeric types are not converted, you can compare the element type and panic or error as necessary:
if v.Type().Elem().Kind() != reflect.Int32 {
...