mergo

README

Mergo

A helper to merge structs and maps in Golang. Useful for configuration default values, avoiding messy if-statements.

Also a lovely comune (municipality) in the Province of Ancona in the Italian region Marche.

Status

It is ready for production use. It works fine although it may use more of testing. Here some projects in the wild using Mergo:

• EagerIO/Stout
• lynndylanhurley/defsynth-api
• russross/canvasassignments
• rdegges/cryptly-api
• casualjim/exeggutor
• divshot/gitling
• RWJMurphy/gorl

Installation

go get github.com/imdario/mergo

// use in your .go code
import (
    "github.com/imdario/mergo"
)

Usage

You can only merge same-type structs with exported fields initialized as zero value of their type and same-types maps. Mergo won't merge unexported (private) fields but will do recursively any exported one. Also maps will be merged recursively except for structs inside maps (because they are not addressable using Go reflection).

if err := mergo.Merge(&dst, src); err != nil {
    // ...
}

Additionally, you can map a map[string]interface{} to a struct (and otherwise, from struct to map), following the same restrictions as in Merge(). Keys are capitalized to find each corresponding exported field.

if err := mergo.Map(&dst, srcMap); err != nil {
    // ...
}

Warning: if you map a struct to map, it won't do it recursively. Don't expect Mergo to map struct members of your struct as map[string]interface{}. They will be just assigned as values.

More information and examples in godoc documentation.

Note: if test are failing due missing package, please execute:

go get gopkg.in/yaml.v1

Contact me

If I can help you, you have an idea or you are using Mergo in your projects, don't hesitate to drop me a line (or a pull request): @im_dario

About

Written by Dario Castañé.

License

BSD 3-Clause license, as Go language.

Documentation

Overview

Package mergo merges same-type structs and maps by setting default values in zero-value fields.

Mergo won't merge unexported (private) fields but will do recursively any exported one. It also won't merge structs inside maps (because they are not addressable using Go reflection).

Usage

From my own work-in-progress project:

type networkConfig struct {
	Protocol string
	Address string
	ServerType string `json: "server_type"`
	Port uint16
}

type FssnConfig struct {
	Network networkConfig
}

var fssnDefault = FssnConfig {
	networkConfig {
		"tcp",
		"127.0.0.1",
		"http",
		31560,
	},
}

// Inside a function [...]

if err := mergo.Merge(&config, fssnDefault); err != nil {
	log.Fatal(err)
}

// More code [...]

Index

• Variables
• func Map(dst, src interface{}) error
• func Merge(dst, src interface{}) error

Variables

var (
	ErrNilArguments                = errors.New("src and dst must not be nil")
	ErrDifferentArgumentsTypes     = errors.New("src and dst must be of same type")
	ErrNotSupported                = errors.New("only structs and maps are supported")
	ErrExpectedMapAsDestination    = errors.New("dst was expected to be a map")
	ErrExpectedStructAsDestination = errors.New("dst was expected to be a struct")
)

Errors reported by Mergo when it finds invalid arguments.

Functions

func Map

func Map(dst, src interface{}) error

Map sets fields' values in dst from src. src can be a map with string keys or a struct. dst must be the opposite: if src is a map, dst must be a valid pointer to struct. If src is a struct, dst must be map[string]interface{}. It won't merge unexported (private) fields and will do recursively any exported field. If dst is a map, keys will be src fields' names in lower camel case. Missing key in src that doesn't match a field in dst will be skipped. This doesn't apply if dst is a map. This is separated method from Merge because it is cleaner and it keeps sane semantics: merging equal types, mapping different (restricted) types.

func Merge

func Merge(dst, src interface{}) error

Merge sets fields' values in dst from src if they have a zero value of their type. dst and src must be valid same-type structs and dst must be a pointer to struct. It won't merge unexported (private) fields and will do recursively any exported field.