future.go

package future

// A Future represents the result of some asynchronous computation.
// Future returns the result of the work as an error, or nil if the work
// was performed successfully.
// Implementers must observe these invariants
// 1. There may be multiple concurrent callers, or Future may be called many
//     times in sequence, it must always return the same value.
// 2. Future blocks until the work has been performed.
type Future func() error

// New returns a Future representing the result of the execution of f.
func New(f func() error) Future {
        ch := make(chan error, 1)
        go func() {
                ch <- f()
        }()
        return func() error {
                result := <-ch
                ch <- result
                return result
        }
}