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package promise
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import (
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	"context"
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	"sync"
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)
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// All provides similar concurrency to JavaScript's Promise.All, however with 1 distinction. []func that
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// are passed in must respect fnCtx cancellation and returns, otherwise All will block even if fnCtx is cancelled.
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func All[V comparable](fnCtx context.Context, fns ...func(fnCtx context.Context) (V, error)) ([]V, []error) {
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	var (
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		wg      = sync.WaitGroup{}
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		results = make([]V, len(fns))
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		errors  = make([]error, len(fns))
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		done    = make(chan struct{}, 1)
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	)
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	wg.Add(len(fns))
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	go func() {
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		wg.Wait()
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		close(done)
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	}()
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	for i, fn := range fns {
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		go func(i int, fn func(context.Context) (V, error)) {
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			defer wg.Done()
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			v, e := fn(fnCtx)
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			if e != nil {
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				errors[i] = e
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				return
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			}
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			results[i] = v
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		}(i, fn)
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	}
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	select {
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	case <-done:
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	case <-fnCtx.Done():
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		// assert that the fn returns first
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		<-done
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	}
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	return results, errors
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}