Resolving named interfaces as map[<name>]<interface>

[defval]

Problem

In case, when I have several named implementations of an interface, I need a simple and clean way to get needed implementation by name.

For example, I have two writer types: file and s3.

inject.New(
  inject.Provide(file.NewDestination, inject.As(new(writer.Destination)), inject.WithName("file")),
  inject.Provide(s3.NewDestination, inject.As(new(writer.Destination)), inject.WithName("s3")),
)

And I need to resolve concrete writer by name.

Proposal

For named providers that will be injected as interfaces create map[<name>]<interface> group.

// NewDestinationWriter
func NewDestinationWriter(destinations map[string]writer.Destination) *DestinationWriter {
  return &DestinationWriter{
    destinations: destinations,
  }
}

// DestinationWriter writes data to destination.
type DestinationWriter {
  destinations map[string]writer.Destination
}

// WriteTo writes data to destination by its name.
func (w *DestinationWriter) WriteTo(destination string, data []byte) error  {
  writer, ok := w.destinations[destination]
  if !ok {
    return fmt.Errorf("destination %s not found", destination)
  }

  return writer.WriteBytes(data)
}