generics.go

package main

import (
	"context"
	"sync"
)

type fanOutResult[K any, R any] struct {
	Key K
	Result R
	Error error
}

type fanOutTask[K any, R any] func(context.Context, K) (R, error)

type fanOutProcessor[K any, R any] struct {
	Tasks   <- chan K
	Handler fanOutTask[K, R]
	Dest    chan <- fanOutResult[K, R]
}

func (f *fanOutProcessor[K, R]) process(ctx context.Context, workers int) {
	var wg sync.WaitGroup

	for i := 0; i < workers; i++ {
		wg.Add(1)
		go f.fanOutWorker(ctx, &wg)
	}

	wg.Wait()
}

func (f *fanOutProcessor[K, R]) fanOutWorker(ctx context.Context, wg *sync.WaitGroup) {
	defer wg.Done()

	for {
		select {
		case task, ok := <-f.Tasks:
			if !ok {
				return
			}

			var msg fanOutResult[K, R]
			msg.Key = task
			msg.Result, msg.Error = f.Handler(ctx, task)
			f.Dest <- msg
		case <-ctx.Done():
			return
		}
	}
}