Method: RxRuby::Observable#scan

Defined in:
lib/rx_ruby/operators/single.rb

#scan(*args, &block) ⇒ Object

Applies an accumulator function over an observable sequence and returns each intermediate result. The optional seed value is used as the initial accumulator value. For aggregation behavior with no intermediate results, see Observable.reduce.



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# File 'lib/rx_ruby/operators/single.rb', line 188

def scan(*args, &block)
  has_seed = false
  seed = nil
  action = nil

  # Argument parsing to support:
  # 1. (seed, Symbol)
  # 2. (seed, &block)
  # 3. (Symbol)
  # 4. (&block)
  if args.length == 2 && args[1].is_a?(Symbol)
    seed = args[0]
    action = args[1].to_proc
    has_seed = true
  elsif args.length == 1 && block_given?
    seed = args[0]
    has_seed = true
    action = block
  elsif args.length == 1 && args[0].is_a?(Symbol)
    action = args[0].to_proc
  elsif args.length == 0 && block_given?
    action = block
  else
    raise ArgumentError.new 'Invalid arguments'
  end

  AnonymousObservable.new do |observer|

    has_accumulation = false
    accumulation = nil
    has_value = false

    new_obs = Observer.configure do |o|
      o.on_next do |x|
        begin
          has_value = true unless has_value

          if has_accumulation
            accumulation = action.call(accumulation, x)
          else
            accumulation = has_seed ? action.call(seed, x) : x
            has_accumulation = true
          end
        rescue => err
          observer.on_error err
          return
        end

        observer.on_next accumulation
      end

      o.on_error(&observer.method(:on_error))

      o.on_completed do
        observer.on_next seed if !has_value && has_seed
        observer.on_completed
      end
    end

    subscribe new_obs
  end
end