func unmarshalTuple()

in marshal.go [2281:2386]
91 lines of code
24 McCabe index (conditional complexity)

func unmarshalTuple(info TypeInfo, data []byte, value interface{}) error {
	if v, ok := value.(Unmarshaler); ok {
		return v.UnmarshalCQL(info, data)
	}

	tuple := info.(TupleTypeInfo)
	switch v := value.(type) {
	case []interface{}:
		for i, elem := range tuple.Elems {
			// each element inside data is a [bytes]
			var p []byte
			if len(data) >= 4 {
				p, data = readBytes(data)
			}
			err := Unmarshal(elem, p, v[i])
			if err != nil {
				return err
			}
		}

		return nil
	}

	rv := reflect.ValueOf(value)
	if rv.Kind() != reflect.Ptr {
		return unmarshalErrorf("can not unmarshal into non-pointer %T", value)
	}

	rv = rv.Elem()
	t := rv.Type()
	k := t.Kind()

	switch k {
	case reflect.Struct:
		if v := t.NumField(); v != len(tuple.Elems) {
			return unmarshalErrorf("can not unmarshal tuple into struct %v, not enough fields have %d need %d", t, v, len(tuple.Elems))
		}

		for i, elem := range tuple.Elems {
			var p []byte
			if len(data) >= 4 {
				p, data = readBytes(data)
			}

			v, err := elem.NewWithError()
			if err != nil {
				return err
			}
			if err := Unmarshal(elem, p, v); err != nil {
				return err
			}

			switch rv.Field(i).Kind() {
			case reflect.Ptr:
				if p != nil {
					rv.Field(i).Set(reflect.ValueOf(v))
				} else {
					rv.Field(i).Set(reflect.Zero(reflect.TypeOf(v)))
				}
			default:
				rv.Field(i).Set(reflect.ValueOf(v).Elem())
			}
		}

		return nil
	case reflect.Slice, reflect.Array:
		if k == reflect.Array {
			size := rv.Len()
			if size != len(tuple.Elems) {
				return unmarshalErrorf("can not unmarshal tuple into array of length %d need %d elements", size, len(tuple.Elems))
			}
		} else {
			rv.Set(reflect.MakeSlice(t, len(tuple.Elems), len(tuple.Elems)))
		}

		for i, elem := range tuple.Elems {
			var p []byte
			if len(data) >= 4 {
				p, data = readBytes(data)
			}

			v, err := elem.NewWithError()
			if err != nil {
				return err
			}
			if err := Unmarshal(elem, p, v); err != nil {
				return err
			}

			switch rv.Index(i).Kind() {
			case reflect.Ptr:
				if p != nil {
					rv.Index(i).Set(reflect.ValueOf(v))
				} else {
					rv.Index(i).Set(reflect.Zero(reflect.TypeOf(v)))
				}
			default:
				rv.Index(i).Set(reflect.ValueOf(v).Elem())
			}
		}

		return nil
	}

	return unmarshalErrorf("cannot unmarshal %s into %T. Accepted types: *struct, []interface{}, *array, *slice, Unmarshaler.", info, value)
}