英文:
Strange type definition syntax in Golang (name, then type, then string literal)
问题
我一直在尝试找出如何使用mgo（Go的MongoDB驱动程序），然后我遇到了这个结构声明：
type Something struct {Id bson.ObjectId "_id,omitempty"Name string}
我不太理解第一个元素（Id）的语法。我知道它被声明为bson.ObjectId类型，但是字符串字面量在那里有什么作用？
我的问题不是关于mgo驱动程序的功能，而是关于这个奇怪的<name> <type> <string_literal>语法。
我在Go规范中找不到任何相关信息，也不知道如何在谷歌上搜索这个。
英文:
I've been trying to find out how to use mgo (MongoDB driver for Go) and I came across this struct declaration:
type Something struct {Id bson.ObjectId "_id,omitempty"Name string}
I don't quite understand the syntax of the first element (Id). I understand that it's being declared as type bson.ObjectId, but what is the string literal doing there?
My question is not about the mgo driver functionality,
but about this strange <name> <type> <string_literal> syntax.
I couldn't find anything on the Go specs, and I don't know how to google this either.
答案1
得分: 58
它在Struct types部分的language specification中有解释：
字段声明后面可以跟一个可选的字符串字面量tag，它成为相应字段声明中所有字段的属性。这些标签通过reflection interface可见，但在其他情况下被忽略。
// 与TimeStamp协议缓冲区对应的结构体。// 标签字符串定义了协议缓冲区字段的编号。struct {microsec uint64 "field 1"serverIP6 uint64 "field 2"process string "field 3"}
英文:
It's explained in the Struct types section of the language specification:
> A field declaration may be followed by an optional string literal
> tag, which becomes an attribute for all the fields in the corresponding field declaration. The tags are made visible through a
> reflection interface but are otherwise ignored.
// A struct corresponding to the TimeStamp protocol buffer.// The tag strings define the protocol buffer field numbers.struct {microsec uint64 "field 1"serverIP6 uint64 "field 2"process string "field 3"}
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