ordone.go

package syncx

import "context"

// OrDone forwards values from in until in closes or ctx is cancelled,
// making a plain `for v := range ch` loop cancellable without nested
// selects at the call site.
//
// The returned channel is unbuffered and is always closed when the
// forwarding goroutine exits, so consumers never block forever and the
// goroutine never leaks. Values already sent by the producer but not yet
// forwarded when ctx is cancelled are dropped.
func OrDone[T any](ctx context.Context, in <-chan T) <-chan T {
	out := make(chan T)

	go func() {
		defer close(out)
		for {
			select {
			case <-ctx.Done():
				return
			case v, ok := <-in:
				if !ok {
					return
				}
				select {
				case out <- v:
				case <-ctx.Done():
					return
				}
			}
		}
	}()

	return out
}