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struct-tag.md

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Use field tags in marshaled structs

Any struct field that is marshaled into JSON, YAML, or other formats that support tag-based field naming should be annotated with the relevant tag.

BadGood
 
type Stock struct {
  Price int
  Name  string
}

bytes, err := json.Marshal(Stock{
  Price: 137,
  Name:  "UBER",
})
 
type Stock struct {
  Price int    `json:"price"`
  Name  string `json:"name"`
  // Safe to rename Name to Symbol.
}

bytes, err := json.Marshal(Stock{
  Price: 137,
  Name:  "UBER",
})

Rationale: The serialized form of the structure is a contract between different systems. Changes to the structure of the serialized form--including field names--break this contract. Specifying field names inside tags makes the contract explicit, and it guards against accidentally breaking the contract by refactoring or renaming fields.