in packages/param/union.go [12:47]
func VariantFromUnion(u reflect.Value) (any, error) {
if u.Kind() == reflect.Ptr {
u = u.Elem()
}
if u.Kind() != reflect.Struct {
return nil, fmt.Errorf("param: cannot extract variant from non-struct union")
}
isUnion := false
nVariants := 0
variantIdx := -1
for i := 0; i < u.NumField(); i++ {
if !u.Field(i).IsZero() {
nVariants++
variantIdx = i
}
if u.Field(i).Type() == paramUnionType {
isUnion = u.Type().Field(i).Anonymous
}
}
if !isUnion {
return nil, fmt.Errorf("param: cannot extract variant from non-union")
}
if nVariants > 1 {
return nil, fmt.Errorf("param: cannot extract variant from union with multiple variants")
}
if nVariants == 0 {
return nil, fmt.Errorf("param: cannot extract variant from union with no variants")
}
return u.Field(variantIdx).Interface(), nil
}