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https://github.com/widmogrod/mkunion
Strongly typed union type in golang.
https://github.com/widmogrod/mkunion
generator go golang golang-library golang-tools reducer traversal union-types visitor-pattern
Last synced: about 18 hours ago
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Strongly typed union type in golang.
- Host: GitHub
- URL: https://github.com/widmogrod/mkunion
- Owner: widmogrod
- License: mit
- Created: 2022-09-26T10:13:54.000Z (over 2 years ago)
- Default Branch: main
- Last Pushed: 2024-07-14T20:55:32.000Z (7 months ago)
- Last Synced: 2024-07-15T13:10:26.415Z (7 months ago)
- Topics: generator, go, golang, golang-library, golang-tools, reducer, traversal, union-types, visitor-pattern
- Language: Go
- Homepage: https://widmogrod.github.io/mkunion/
- Size: 4.9 MB
- Stars: 5
- Watchers: 2
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE
- Roadmap: docs/roadmap.md
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README
# Welcome to MkUnion
[](https://pkg.go.dev/github.com/widmogrod/mkunion)
[](https://goreportcard.com/report/github.com/widmogrod/mkunion)
[](https://codecov.io/gh/widmogrod/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
```go title="example/vehicle.go"
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](https://widmogrod.github.io/mkunion/getting_started/) to learn more.