Function Fetch

vm/runtime/runtime.go:21–102

(from, i any)

}

func Fetch(from, i any) any {
	v := reflect.ValueOf(from)
	if v.Kind() == reflect.Invalid {
		panic(fmt.Sprintf("cannot fetch %v from %T", i, from))
	}

	// Methods can be defined on any type.
	if v.NumMethod() > 0 {
		if methodName, ok := i.(string); ok {
			method := v.MethodByName(methodName)
			if method.IsValid() {
				return method.Interface()
			}
		}
	}

	// Structs, maps, and slices can be access through a pointer or through
	// a value, when they are accessed through a pointer we don't want to
	// copy them to a value.
	// De-reference everything if necessary (interface and pointers)
	v = deref.Value(v)

	switch v.Kind() {
	case reflect.Array, reflect.Slice, reflect.String:
		index := ToInt(i)
		l := v.Len()
		if index < 0 {
			index = l + index
		}
		if index < 0 || index >= l {
			panic(fmt.Sprintf("index out of range: %v (array length is %v)", index, l))
		}
		value := v.Index(index)
		if value.IsValid() {
			return value.Interface()
		}

	case reflect.Map:
		var value reflect.Value
		if i == nil {
			value = v.MapIndex(reflect.Zero(v.Type().Key()))
		} else {
			value = v.MapIndex(reflect.ValueOf(i))
		}
		if value.IsValid() {
			return value.Interface()
		} else {
			elem := reflect.TypeOf(from).Elem()
			return reflect.Zero(elem).Interface()
		}

	case reflect.Struct:
		fieldName := i.(string)
		t := v.Type()
		key := fieldCacheKey{
			t: t,
			f: fieldName,
		}