Idea for multivariant structs in go-yaml (for zrepl)

multi-struct-yaml-example.go

package main

import (
	"fmt"
	"log"

	"gopkg.in/yaml.v2"
)

// An example showing how to unmarshal embedded
// structs from YAML.

type Hooks struct {
	PreHook  string               `yaml:"pre"`
	PostHook string               `yaml:"post"`
	Timeout  TimeoutSingleOrMulti `yaml:"timeout"`
}

type TimeoutSingleOrMulti struct {
	Ret interface{}
}

type Timeouts struct {
	Pre  int `yaml:"pre"`
	Post int `yaml:"post"`
}

func (timeouts *TimeoutSingleOrMulti) UnmarshalYAML(unmarshal func(interface{}) error) error {
	var globalTimeout int
	var multiTimeout Timeouts

	if err := unmarshal(&globalTimeout); err != nil {
		if err := unmarshal(&multiTimeout); err != nil {
			return err
		}
	} else {
		multiTimeout.Pre = globalTimeout
		multiTimeout.Post = globalTimeout
		timeouts.Ret = multiTimeout
	}

	timeouts.Ret = multiTimeout
	return nil
}

/*
var data = `
pre: foo.sh
post: bar.sh
timeout:
    pre: 30
    post: 60
`
*/

var data = `
pre: foo.sh
post: bar.sh
timeout: 90
`

func main() {
	var hooks Hooks

	err := yaml.Unmarshal([]byte(data), &hooks)
	if err != nil {
		log.Fatalf("cannot unmarshal data: %v", err)
	}
	fmt.Printf("%+v\n", hooks)
}