Class: LookAheadIterator

Inherits:
Object
  • Object
show all
Includes:
Enumerable
Defined in:
lib/look_ahead_iterator.rb,
lib/look_ahead_iterator/version.rb

Constant Summary collapse

VERSION = 
"0.0.1"

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(enumerable, options = {}) ⇒ LookAheadIterator

A LookAheadIterator can be created from any enumerable object.

Options:

  • :stop : If true, the iteration will stop by throwing StopIteration like other external iterators. This will end a loop.

   Otherwise the user must check of end of iteration by

  • :end : is used to define a special value to be returned if the iteration has ended (or when looking beyond the end of the collection). By default it is nil.



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# File 'lib/look_ahead_iterator.rb', line 16

def initialize(enumerable, options = {})
  @end_value = options[:end]
  @stop = options[:stop]
  @iterator = enumerable.each
  @iterator_ended = false
  @buffer = []
  @current = nil
  @ended = false
end

Instance Attribute Details

#current ⇒ Object (readonly)

Returns the value of attribute current.



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# File 'lib/look_ahead_iterator.rb', line 26

def current
  @current
end

#end_value ⇒ Object (readonly)

Returns the value of attribute end_value.



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# File 'lib/look_ahead_iterator.rb', line 26

def end_value
  @end_value
end

Instance Method Details

#each ⇒ Object 



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# File 'lib/look_ahead_iterator.rb', line 28

def each
  if @stop
    loop do
      yield self.next
    end
  else
    yield self.next while next?
  end
end

#ended? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/look_ahead_iterator.rb', line 60

def ended?
  # If @end_value cannot be contained in the collection,
  # then this is equivalent to:
  #   @buffer.empty? && @current = @end_value
  @ended
end

#is_end?(value) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/look_ahead_iterator.rb', line 90

def is_end?(value)
  value == @end_value
end

#is_valid?(value) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/look_ahead_iterator.rb', line 94

def is_valid?(value)
  value != @end_value
end

#look_ahead(n = 1) ⇒ Object

This method is used to obtained the next value to be returned by each. If a parameter n is passed the value to be returned after n calls to each is returned. The value 0 can be used to return the current value (from the previous call to each),



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# File 'lib/look_ahead_iterator.rb', line 79

def look_ahead(n=1)
  raise "Can't look back!" if n < 0
  return @current if n == 0

  while n > @buffer.size && !@iterator_ended
    value = next_or_end
    @buffer << value unless @iterator_ended
  end
  n <= @buffer.size ? @buffer[n-1] : @end_value
end

#next ⇒ Object 



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# File 'lib/look_ahead_iterator.rb', line 40

def next
  if @buffer.size > 0
    @current = @buffer.shift
  else
    if @stop
      begin
        @current = @iterator.next
      rescue StopIteration
        @iterator_ended = @ended = true
        @current = @end_value
        raise
      end
    else
      @current = next_or_end
      @ended = @iterator_ended
      @current
    end
  end
end

#next? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/look_ahead_iterator.rb', line 67

def next?
  # If @end_value cannot be contained in the collection,
  # then this is equivalent to:
  #   !ended? && (look_ahead(1) != @end_value)
  !ended? && (look_ahead(1); !(@iterator_ended && @buffer.size==0))
end