FAQ

• Should I use Flow or Parallel?
• Does cff.Flow allow multiple values of the same type?

Should I use Flow or Parallel?

Flow runs interdependent tasks. That is, the output of a task is typically the input of another, with very few leaf tasks--tasks whose outputs are consumed with cff.Results.

Parallel, on the other hand, runs independent tasks. If you find yourself managing groups of goroutines with sync.WaitGroup, consider using cff.Parallel instead.

// Before
var wg sync.WaitGroup
for _, url := range urls {
	wg.Add(1)
	go func(url string) {
		defer wg.Done()

		res, err := http.Get(url)
		// ...
	}(url)
}

// After
cff.Parallel(ctx,
	cff.Slice(func(url string) error {
		res, err := http.Get(url)
		// ...
	}, urls),
)

See also What can I use cff for?.

Does cff.Flow allow multiple values of the same type?

No, cff.Flow does not yet allow multiple values of the same type to be returned by different tasks. Each type must be returned by exactly one task in the flow.

If you have need of this, you can work around this limitation by defining temporary type wrappers around the return type and casting to those values within the flow.

// Given,
//   func (*UserClient) GetUser(...) (*User, error)

// Define wrappers for the different kinds of User objects we need.
type (
  RiderUser  User
  DriverUser User
)

err := cff.Flow(ctx,
  // ...
  cff.Task(func(...) (*RiderUser, error) {
    u, err := userClient.GetUser(...)
    return (*RiderUser)(u)
  }),
  cff.Task(func(...) (*DriverUser, error) {
    u, err := userClient.GetUser(...)
    return (*DriverUser)(u)
  }),
)