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golang 'future' example (https://en.wikipedia.org/wiki/Futures_and_promises)
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| package main | |
| import ( | |
| "encoding/json" | |
| "fmt" | |
| "log" | |
| "net/http" | |
| "sync" | |
| ) | |
| type CurrencyRateFuture func() (float64, error) | |
| func NewCurrencyRateFuture() CurrencyRateFuture { | |
| var ( | |
| val float64 | |
| err error | |
| mtx sync.Mutex | |
| ) | |
| mtx.Lock() | |
| go func() { | |
| defer mtx.Unlock() | |
| v, e := ReadCurrencyRateFromRBC() | |
| val = v | |
| if e != nil { | |
| err = fmt.Errorf("reading currency rate: %s", e) | |
| } | |
| }() | |
| return func() (float64, error) { | |
| mtx.Lock() | |
| defer mtx.Unlock() | |
| return val, err | |
| } | |
| } | |
| func main() { | |
| currRateFuture := NewCurrencyRateFuture() | |
| rate, err := currRateFuture() | |
| if err != nil { | |
| panic(err) | |
| } | |
| fmt.Println(rate) | |
| rate, err = currRateFuture() | |
| if err != nil { | |
| panic(err) | |
| } | |
| fmt.Println(rate) | |
| } | |
| func ReadCurrencyRateFromRBC() (float64, error) { | |
| log.Print("currency rate reading begin") | |
| defer log.Print("currency rate reading end") | |
| const convAPI = "https://cash.rbc.ru/cash/json/converter_currency_rate/?currency_from=USD¤cy_to=RUR&source=cbrf&sum=2&date=" | |
| resp, err := http.Get(convAPI) | |
| if err != nil { | |
| return 0, err | |
| } | |
| defer resp.Body.Close() | |
| if resp.StatusCode != 200 { | |
| return 0, fmt.Errorf("bad HTTP status code: %d", resp.StatusCode) | |
| } | |
| reply := struct { | |
| Data struct{ Rate1 float64 } | |
| Status int | |
| }{} | |
| err = json.NewDecoder(resp.Body).Decode(&reply) | |
| if err != nil { | |
| return 0, fmt.Errorf("bad API response: %s", err) | |
| } | |
| if reply.Status != 200 { | |
| return 0, fmt.Errorf("bad API reply status code: %d", reply.Status) | |
| } | |
| return reply.Data.Rate1, nil | |
| } |
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