Go结构字段的第三个参数是什么？

Question

type Config struct {
    CommitIndex uint64 `json:"commitIndex"`
    // TODO decide what we need to store in peer struct
    Peers []*Peer `json:"peers"`
}

I understand what the first two columns are,but what is json:"commitIndex"?

Answer 1

It's called a struct tag, they can be parsed using the reflect package at runtime.

From https://golang.org/ref/spec#Struct_types:

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.

Some packages that use reflection like json and xml use tags to handle special cases better.