1# mapstructure [![Godoc](https://godoc.org/github.com/mitchellh/mapstructure?status.svg)](https://godoc.org/github.com/mitchellh/mapstructure) 2 3mapstructure is a Go library for decoding generic map values to structures 4and vice versa, while providing helpful error handling. 5 6This library is most useful when decoding values from some data stream (JSON, 7Gob, etc.) where you don't _quite_ know the structure of the underlying data 8until you read a part of it. You can therefore read a `map[string]interface{}` 9and use this library to decode it into the proper underlying native Go 10structure. 11 12## Installation 13 14Standard `go get`: 15 16``` 17$ go get github.com/mitchellh/mapstructure 18``` 19 20## Usage & Example 21 22For usage and examples see the [Godoc](http://godoc.org/github.com/mitchellh/mapstructure). 23 24The `Decode` function has examples associated with it there. 25 26## But Why?! 27 28Go offers fantastic standard libraries for decoding formats such as JSON. 29The standard method is to have a struct pre-created, and populate that struct 30from the bytes of the encoded format. This is great, but the problem is if 31you have configuration or an encoding that changes slightly depending on 32specific fields. For example, consider this JSON: 33 34```json 35{ 36 "type": "person", 37 "name": "Mitchell" 38} 39``` 40 41Perhaps we can't populate a specific structure without first reading 42the "type" field from the JSON. We could always do two passes over the 43decoding of the JSON (reading the "type" first, and the rest later). 44However, it is much simpler to just decode this into a `map[string]interface{}` 45structure, read the "type" key, then use something like this library 46to decode it into the proper structure. 47