Welcome to MkUnion

About

Strongly typed union type in golang with generics*.

• with exhaustive pattern matching support
• with json marshalling including generics
• and as a bonus, can generate compatible typescript types for end-to-end type safety in your application

Why

Historically in languages without union types like golang, unions were solved either by using Visitor pattern, or using iota and switch statement, or other workarounds.

Visitor pattern requires a lot of boiler plate code and hand crafting of the Accept method for each type in the union. iota and switch statement is not type safe and can lead to runtime errors, especially when new type is added and not all case statements are updated.

On top of that, any data marshalling like to/from JSON requires additional, hand crafted code, to make it work.

MkUnion solves all of those problems, by generating opinionated and strongly typed meaningful code for you.

Example

package example

//go:generate mkunion

// union declaration
//go:tag mkunion:"Vehicle"
type (
	Car struct {
		Color  string
		Wheels int
	}
	Plane struct {
		Color   string
		Engines int
	}
	Boat struct {
		Color      string
		Propellers int
	}
)

func CalculateFuelUsage(v Vehicle) int {
	// example of pattern matching over Vehicle union type
	return MatchVehicleR1(
		v,
		func(x *Car) int {
			return x.Wheels * 2
		},
		func(x *Plane) int {
			return x.Engines * 10
		},
		func(x *Boat) int {
			return x.Propellers * 5
		},
	)
}

func ExampleToJSON() {
    var vehicle Vehicle = &Car{
        Color:  "black",
        Wheels: 4,
    }
    result, _ := shared.JSONMarshal(vehicle)
    fmt.Println(string(result))
    // Output: {"$type":"example.Car","example.Car":{"Color":"black","Wheels":4}}
}

func ExampleFromJSON() {
	input := []byte(`{"$type":"example.Car","example.Car":{"Color":"black","Wheels":4}}`)
	vehicle, _ := shared.JSONUnmarshal[Vehicle](input)
	fmt.Printf("%#v", vehicle)
	// Output: &example.Car{Color:"black", Wheels:4}
}

Next

• Read getting started to learn more.