Fan-out with errgroup and shared cancellation

                  package service

import (
  "context"

  "golang.org/x/sync/errgroup"
)

type User struct{ ID string }
type Billing struct{ Plan string }
type Features struct{ Flags []string }

type Clients interface {
  FetchUser(ctx context.Context, id string) (User, error)
  FetchBilling(ctx context.Context, id string) (Billing, error)
  FetchFeatures(ctx context.Context, id string) (Features, error)
}

func Aggregate(ctx context.Context, c Clients, id string) (User, Billing, Features, error) {
  g, ctx := errgroup.WithContext(ctx)

  var u User
  var b Billing
  var f Features

  g.Go(func() error {
    var err error
    u, err = c.FetchUser(ctx, id)
    return err
  })
  g.Go(func() error {
    var err error
    b, err = c.FetchBilling(ctx, id)
    return err
  })
  g.Go(func() error {
    var err error
    f, err = c.FetchFeatures(ctx, id)
    return err
  })

  if err := g.Wait(); err != nil {
    return User{}, Billing{}, Features{}, err
  }
  return u, b, f, nil
}