What is the usage of backtick in golang structs definition? [duplicate]

Answer 1

They are tags:

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 and take part in type identity for structs 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"
}

See this question and answer for a more detailed explanation and answer.

The back quotes are used to create raw string literals which can contain any type of character:

Raw string literals are character sequences between back quotes ``. Within the quotes, any character is legal except back quote.

Answer 2

You can add extra meta information to Go structs in the form of tags. Here are some examples of use cases.

In this case, the json:"gateway" is used by the json package to encode the value of Gateway into the key gateway in the corresponding json object.

Example:

n := NetworkInterface{
   Gateway : "foo"
}
json.Marshal(n)
// will output `{"gateway":"foo",...}`