这个函数return哪里不报错？

Question

我正在围绕数据存储构建一个包装器 GetAll function and I have a hard time finding where this function returns a non-error. It seems to me that unless there is any other error (i.e. when it breaks on Done) 它 returns errFieldMismatch 我认为这是不正确的。

func (q *Query) GetAll(c context.Context, dst interface{}) ([]*Key, error) {
    var (
        dv               reflect.Value
        mat              multiArgType
        elemType         reflect.Type
        errFieldMismatch error
    )
    if !q.keysOnly {
        dv = reflect.ValueOf(dst)
        if dv.Kind() != reflect.Ptr || dv.IsNil() {
            return nil, ErrInvalidEntityType
        }
        dv = dv.Elem()
        mat, elemType = checkMultiArg(dv)
        if mat == multiArgTypeInvalid || mat == multiArgTypeInterface {
            return nil, ErrInvalidEntityType
        }
    }

    var keys []*Key
    for t := q.Run(c); ; {
        k, e, err := t.next()
        if err == Done {
            break
        }
        if err != nil {
            return keys, err
        }
        if !q.keysOnly {
            ev := reflect.New(elemType)
            if elemType.Kind() == reflect.Map {
                // This is a special case. The zero values of a map type are
                // not immediately useful; they have to be make'd.
                //
                // Funcs and channels are similar, in that a zero value is not useful,
                // but even a freshly make'd channel isn't useful: there's no fixed
                // channel buffer size that is always going to be large enough, and
                // there's no goroutine to drain the other end. Theoretically, these
                // types could be supported, for example by sniffing for a constructor
                // method or requiring prior registration, but for now it's not a
                // frequent enough concern to be worth it. Programmers can work around
                // it by explicitly using Iterator.Next instead of the Query.GetAll
                // convenience method.
                x := reflect.MakeMap(elemType)
                ev.Elem().Set(x)
            }
            if err = loadEntity(ev.Interface(), e); err != nil {
                if _, ok := err.(*ErrFieldMismatch); ok {
                    // We continue loading entities even in the face of field mismatch errors.
                    // If we encounter any other error, that other error is returned. Otherwise,
                    // an ErrFieldMismatch is returned.
                    errFieldMismatch = err
                } else {
                    return keys, err
                }
            }
            if mat != multiArgTypeStructPtr {
                ev = ev.Elem()
            }
            dv.Set(reflect.Append(dv, ev))
        }
        keys = append(keys, k)
    }
    return keys, errFieldMismatch
}

Answer 1

默认为return errFieldMismatch，在函数顶部声明，但不初始化。

如果在迭代过程中的任何一点都没有 ErrFieldMismatch，errFieldMismatch 最后仍将是 nil，因此 GetAll 将 return 一个 nil 错误。

这个函数return哪里不报错？

Where does this function return non error?

go

google-cloud-datastore