Polymorphic Optics #

package main

import (
	"fmt"
	. "github.com/spearson78/go-optic"
	"github.com/spearson78/go-optic/expr"
)

// V1 data types
type BlogPost struct {
	author string
	title string
	content string
	comments []Comment
	ratings []Rating
}
  
type Comment struct {
	author string
	title string
	content string
}
  
type Rating struct {
	author string
	stars int
}
  
// V2 data types
type BlogPostV2 struct {
	author string
	title string
	content string
	comments []Comment
	ratings []RatingV2
}
  
type RatingV2 struct {
	author string
	stars float64
}
  
func ExamplePolymorphism() {

	upgradeBlogRatings := LensP[BlogPost, BlogPostV2, []Rating, []RatingV2](
		func(source BlogPost) []Rating {
			return source.ratings
		},
		func(source BlogPost, focus []RatingV2) BlogPostV2 {
			return BlogPostV2{
				//Retain the fields that don't need an upgrade
				author: source.author,
				title: source.title,
				content: source.content,
				comments: source.comments,
	  
				//Use the upgraded focus for ratings
				ratings: focus,
			}
		},
		ExprCustom("upgradeBlogRatings"),
	)
  
	upgradeTraverseSlice := TraverseSliceP[Rating, RatingV2]()
	  
	upgradeRatingStars := LensP[Rating, RatingV2, int, float64](
		func(source Rating) int {
			return source.stars
		},
		func(source Rating, focus float64) RatingV2 {
			return RatingV2{
				author: source.author,
				stars: focus,
			}
		},
		ExprCustom("upgradeRatingStars"),
	)
  
	upgradeOptic := Compose3(
		upgradeBlogRatings,
		upgradeTraverseSlice,
		upgradeRatingStars,
	)
  
	var result BlogPostV2 = MustModify(
		upgradeOptic, 
		IsoCast[int, float64](),
		BlogPost{
			author: "Max Mustermann",
			title: "Polymorphic Optics",
			content: "Lorem ipsum",
			comments: []Comment{},
			ratings: []Rating{
				{
					author: "Max Mustermann",
					rating: 5,
				},
		},
	})
  
	fmt.Println(result)
  
	//Output:
	//{Max Mustermann Polymorphic Optics Lorem ipsum [] [{Max Mustermann 0.5}]}
}