Comparison to Our Original Approach

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package main

import "context"

type Group struct {
	errc   chan error
	cancel context.CancelCauseFunc
	count  int
}

func NewGroup(cancel context.CancelCauseFunc) *Group {
	return &Group{errc: make(chan error, 1), cancel: cancel}
}

func (g *Group) Go(f func() error) {
	g.count++
	go func() {
		g.errc <- f()
	}()
}

func (g *Group) Wait() error {
	var err error
	for range g.count {
		if e := <-g.errc; e != nil && err == nil {
			err = e
			g.cancel(e)
		}
	}

	return err
}

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package main

import (
	"context"

	"fillmore-labs.com/blog/structured/pkg/task"
)

func doWork(ctx context.Context) error {
	ctx, cancel := context.WithCancelCause(ctx)
	defer cancel(nil)

	g := NewGroup(cancel)

	g.Go(func() error {
		return task.Task(ctx, "task1", processingTime/3, nil)
	})

	g.Go(func() error {
		return task.Task(ctx, "task2", processingTime/2, errFail)
	})

	g.Go(func() error {
		return task.Task(ctx, "task3", processingTime, nil)
	})

	return g.Wait()
}