class

Cute::Sink(T)

Inherits Cute::Signal / Reference / Object

Base class for sinks. A sink acts like a Signal, and is used to emit upon fulfilling sink-specific conditions.

Usage

A sink really acts like a Signal, because it is one. This means, you connect to it using #on. You can even chain sinks! You connect a Sink to a Signal by passing it as argument to #on:

btn = Button.new
sink = Cute::BufferSink(Nil).new(size: 2)
btn.clicked.on(sink)
sink.on { puts "Clicked twice!" }

The generic argument to the class is what the signal emits as type. The example above uses the Button class, used as example for Cute.signal. Its clicked signal however had the two arguments x : Int32, y : Int32! If you want to collect these, you have to pass the type(s) as generic argument:

btn = Button.new
sink = Cute::BufferSink(Tuple(Int32, Int32)).new(size: 2)
btn.clicked.on(sink)
sink.on { |collected| puts "Clicked twice, positions: #{collected}" }

Note: When you're using a sink to collect from a signal passing multiple arguments you have to use a Tuple as type to collect them all at once.

Note: To collect a signal with no arguments, use Nil, like in Cute::BufferSink(Nil).new(...)

In the above example, the collected argument to the #on block to the sink will contain all collected signal emission arguments since the last emission.

Writing synchronously using asynchronous signals

Another great use-case using a sink with the Signal#wait method. Let's assume your program downloads data in parallel from the Internet, showing progress to the user using signals, and want to process the results at once after finishing all of them:

def download_all(urls) : Cute::Sink
  sink = Cute::BufferSink(HttpResponse).new(size: urls.size) # Create a sink
  urls.each do |url|
    down = AsynchronousDownloader.new(url)
    down.progress.on { |percent| show_progress(down, percent) } # Update the UI
    down.finished.on(sink)                                      # Once finished, notify the sink
  end
  sink # And return the sink
end

With that method in place, it's really easy to write synchronous code to process the results:

sink = download_all(the_urls) # Start the asynchronous download
results = sink.wait           # Use Signal#wait to wait
# results will be a `Array(HttpResponse)`
pp results # Do something with the results.

Following a pattern like this makes it easy to inform your user about progress, while being able to easily write synchronous code: The best of both worlds.

Manually using a sink

It may be useful to manually provide data into a sink. This is useful to convert results from a non-signal based into a signal based one.

For this, you can use Sink#notify:

sink = Cute::BufferSink(Int32).new(size: 10) # Set it up
sink.on { |data| puts "Calculation results: #{data}" }

10.times { sink.notify rand(1..100) } # Calculate and provide data