英文:
In golang, how to embed on custom type?
问题
我有自定义类型Int64Array，Channel和ChannelList，如下所示：
type Int64Array []int64
func (ia *Int64Array) Scan(src interface{}) error {
rawArray := string(src.([]byte))
if rawArray == "{}" {
*ia = []int64{}
} else {
matches := pgArrayPat.FindStringSubmatch(rawArray)
if len(matches) > 1 {
for _, item := range strings.Split(matches[1], ",") {
i, _ := strconv.ParseInt(item, 10, 64)
*ia = append(*ia, i)
}
}
}
return nil
}
func (ia Int64Array) Value() (driver.Value, error) {
var items []string
for _, item := range ia {
items = append(items, strconv.FormatInt(int64(item), 10))
}
return fmt.Sprintf("{%s}", strings.Join(items, ",")), nil
}
type Channel int64
type ChannelList []Channel
我该如何将Int64Array嵌入到ChannelList中，以便可以在其上调用Scan和Value方法？我尝试了以下代码：
type ChannelList []Channel {
Int64Array
}
但是我得到了语法错误。重要的是确保ChannelList的项是Channel类型的。如果无法通过嵌入实现这一点，我可以创建独立的函数供ChannelList和Int64Array同时调用。
英文:
I have custom types Int64Array, Channel and ChannelList like:
type Int64Array []int64
func (ia *Int64Array) Scan(src interface{}) error {
rawArray := string(src.([]byte))
if rawArray == "{}" {
*ia = []int64{}
} else {
matches := pgArrayPat.FindStringSubmatch(rawArray)
if len(matches) > 1 {
for _, item := range strings.Split(matches[1], ",") {
i, _ := strconv.ParseInt(item, 10, 64)
*ia = append(*ia, i)
}
}
}
return nil
}
func (ia Int64Array) Value() (driver.Value, error) {
var items []string
for _, item := range ia {
items = append(items, strconv.FormatInt(int64(item), 10))
}
return fmt.Sprintf("{%s}", strings.Join(items, ",")), nil
}
type Channel int64
type ChannelList []Channel
How can I embed Int64Array to ChannelList such that I can call Scan and Value methods on it? I tried the following:
type ChannelList []Channel {
Int64Array
}
but I'm getting syntax error. What's important is to make sure ChannelList items are of type Channel, if this isn't possible via embedding I might just create stand-alone functions to be called by both ChannelList and Int64Array.
答案1
得分: 3
匿名字段（或嵌入字段）出现在结构体中（参见struct类型），而不是类型别名（或“类型声明”）中。
你不能在另一个类型声明中嵌入类型声明。
此外，正如“Go：使用指向数组的指针”的答案所示，你不应该使用指向切片的指针，而应直接使用切片本身（按值传递）。
Wessie在评论中友好地指出，(ia *Int64Array) Scan()使用指向切片的指针来改变所引用的底层数组。
我更喜欢返回另一个切片而不是改变现有的切片。
话虽如此，Golang代码审查确实提到：
> 如果接收器是struct、array或slice，并且其中任何一个元素是指向可能发生变化的内容的指针，请优先使用指针接收器，因为这将使意图对读者更加清晰。
英文:
An anonymous (or embedded field) is found in a struct (see struct type), not in a type alias (or "type declaration").
You cannot embed a type declaration within another type declaration.
Plus, as illustrated by the answers to "Go: using a pointer to array", you shouldn't be using pointers to slice, use directly the slice themselves (passed by value).
Wessie kindly points out in the comments that (ia *Int64Array) Scan() uses pointer to a slice in order to mutate the underlying array referenced by said slice.
I would prefer returning another slice instead of mutating the existing one.
That being said, the Golang Code Review does mention:
> If the receiver is a struct, array or slice and any of its elements is a pointer to something that might be mutating, prefer a pointer receiver, as it will make the intention more clear to the reader.
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