What Does ``, ``, `` Mean in Go Struct Declarations?

Understanding the Unusual Syntax: , , in Go Structs

In Golang, struct declarations often incorporate a peculiar syntax involving a name, type, and a string literal. This uncommon pattern, exemplified by the code snippet below, has puzzled many developers.

type Something struct {
    Id bson.ObjectId "_id,omitempty"
    Name string
}

To decode this syntax, it's essential to delve into the Go language specification. The key lies in the "Struct Types" section. It unveils that a field declaration can be accompanied by an optional string literal known as a "tag". This tag serves as an attribute for all fields within the corresponding field declaration.

Conventionally, these tags are exposed through the reflection interface, rendering them valuable for introspection and serialization purposes. However, they remain largely invisible in the general context of the program.

// A struct conforming to the TimeStamp protocol buffer.
// The appended string literals denote the protocol buffer field numbers.
struct {
    microsec  uint64 "field 1"
    serverIP6 uint64 "field 2"
    process   string "field 3"
}

In essence, the syntax ", , " in Go structs utilizes tags to assign attributes to fields. These tags facilitate reflection and serialization, enabling developers to augment their structs with metadata.

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