Command Lists (Automatic Result Types)

[Phrogz]

Implements command lists in a manner that (a) allows various results to be interleaved and still return the correct types, and (b) allows playlist objects to be used directly in a command list.

# Do not parse response (for speed)
@mpd.command_list do
  add song
  volume 50
  shuffle
end

# Array of values from each response line
ids = @mpd.command_list(results:true) do
  addid song1
  addid song2
end
#=> [113,114]

# Arrays of Songs
songs = @mpd.command_list(results:true) do
  where genre:'electronic'
  where genre:'trance'
end
#=> [
#=>    [ <MPD::Song>, <MPD::Song>, … ],
#=>    [ <MPD::Song>, <MPD::Song>, … ]
#=> ]

# Array of Playlists
results = @mpd.command_list(results:true) do
  clear
  where({genre:'electronic'},{add:true})
  save 'new-playlist'
  playlists
end
#=> [
#=>    [ <MPD::Playlist>, <MPD::Playlist>, … ]
#=> ]

# Using Playlist inside Command List
def shuffle_playlist( playlist )
  song_count = playlist.songs.length
  @mpd.command_list do
    (song_count-1).downto(1){ |i| playlist.move i, rand(i+1) }
  end
end

This has a small class used for the DSL, but that is not strictly necessary. Though it doesn't look as nice, the following code works:

@mpd.command_list do
  @mpd.clear
  @mpd.addid my_song
  @mpd.songs
end

…because starting a command_list causes all other commands to ignore the response, but to record the commands used for later parsing of the command_list results.

[archseer]

Sorry for the long wait, it's quite a big PR. I'm a bit anxious to just merge it, but the tests you've added seem sound. If you address the minor comments I'll merge this :)

[LevitatingBusinessMan]

I know its been a whole Ruby version but what needs to be done to get this merged?