Question

我有这个示例代码，它基本上只是一些使用mdii文件的基本类

class Array
    def to_midi(file, note_length='eighth')

        midi_max = 108.0
        midi_min = 21.0

        low, high = min, max
        song = MIDI::Sequence.new

        # Create a new track to hold the melody, running at 120 beats per minute.
        song.tracks << (melody = MIDI::Track.new(song))
        melody.events << MIDI::Tempo.new(MIDI::Tempo.bpm_to_mpq(120))

        # Tell channel zero to use the "piano" sound.
        melody.events << MIDI::ProgramChange.new(0, 0)

        # Create a series of note events that play on channel zero.
        each do |number|
            midi_note = (midi_min + ((number-midi_min) * (midi_max-low)/high)).to_i
            melody.events << MIDI::NoteOnEvent.new(0, midi_note, 127, 0)
            melody.events << MIDI::NoteOffEvent.new(0, midi_note, 127,
            song.note_to_delta(note_length))
        end

        open(file, 'w') { |f| song.write(f) }
    end
end
class TimedTrack < MIDI::Track
    MIDDLE_C = 60
    @@channel_counter=0

    def initialize(number, song)
        super(number)
        @sequence = song
        @time = 0
        @channel = @@channel_counter
        @@channel_counter += 1
    end

    # Tell this track's channel to use the given instrument, and
    # also set the track's instrument display name.
    def instrument=(instrument)
        @events << MIDI::ProgramChange.new(@channel, instrument)
        super(MIDI::GM_PATCH_NAMES[instrument])
    end

      # Add one or more notes to sound simultaneously. Increments the per-track
      # timer so that subsequent notes will sound after this one finishes.
    def add_notes(offsets, velocity=127, duration='quarter')
        offsets = [offsets] unless offsets.respond_to? :each
        offsets.each do |offset|
            event(MIDI::NoteOnEvent.new(@channel, MIDDLE_C + offset, velocity))
        end
        @time += @sequence.note_to_delta(duration)
        offsets.each do |offset|
            event(MIDI::NoteOffEvent.new(@channel, MIDDLE_C + offset, velocity))
        end
        recalc_delta_from_times
    end

      # Uses add_notes to sound a chord (a major triad in root position), using the
      # given note as the low note. Like add_notes, increments the per-track timer.
    def add_major_triad(low_note, velocity=127, duration='quarter')
        add_notes([0, 4, 7].collect { |x| x + low_note }, velocity, duration)
    end

    private

        def event(event)
            @events << event
            event.time_from_start = @time
        end
end

除了使用<<运算符的行之外，大多数情况对我来说都很有意义，在我的所有研究中，使用<<的唯一原因是当你定义一个类时单身人士那么具体是在这段代码中使用<<？

Answer 1

来自https://github.com/jimm/midilib：
MIDI::Track是包含一系列事件的轨道。

因此，使用<<，您可以向赛道添加活动。它是一样的 melody.events.push(MIDI::NoteOnEvent.new(0, midi_note, 127, 0))

<<也可用于位移操作

http://calleerlandsson.com/2014/02/06/rubys-bitwise-operators/

Answer 2

<<运算符可以用于按位运算（这里不太可能），也可能在类中重载以匹配某些行为。在这种情况下，（可能）有Array个对象，因此event通过此运算符被推入@events数组。有关此用例can be found here的更多信息。

请注意，将来你可以遇到使用此运算符的其他情况，而不是每次都表示同样的事情 - 它取决于库创建者。现在想到的另一个用例可以是ActiveRecord Relationships，如has_many，您也可以使用此运算符立即将对象推送到关系并保存。有关此内容的更多信息，请参阅api docs here。快速样本：

class User < ActiveRecord::Base
  has_many :posts
end

class Post < ActiveRecord::Base
  belongs_to :user
end

然后在代码的某个地方你可以使用：

@post = Post.find(10)
@user = User.find(1)
@user.posts << @post
# automatically save the @post object with updated foreign key

＆＃39;＆lt;＆lt;＆lt;＆lt;＆lt;＆lt;＆lt;＆＃红宝石的操作员

2 个答案: