Class: Generator

Inherits:
Object
  • Object
show all
Includes:
Enumerable
Defined in:
lib/rubysl/generator/generator.rb

Overview

Generator converts an internal iterator (i.e. an Enumerable object) to an external iterator.

Note that it is not very fast since it is implemented using continuations, which are currently slow.

Example

require 'generator'

# Generator from an Enumerable object
g = Generator.new(['A', 'B', 'C', 'Z'])

while g.next?
  puts g.next
end

# Generator from a block
g = Generator.new { |g|
  for i in 'A'..'C'
    g.yield i
  end

  g.yield 'Z'
}

# The same result as above
while g.next?
  puts g.next
end

Instance Method Summary collapse

Constructor Details

#initialize(enum = nil, &block) ⇒ Generator

Creates a new generator either from an Enumerable object or from a block.

In the former, block is ignored even if given.

In the latter, the given block is called with the generator itself, and expected to call the yield method for each element.



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# File 'lib/rubysl/generator/generator.rb', line 69

def initialize(enum=nil, &block)
  if enum
    @block = proc do |g|
      enum.each { |x| g.yield x }
    end
  else
    @block = block
  end

  @index = 0
  @queue = []

  @done = false

  @fiber = Rubinius::Fiber.new do
    @block.call(self)
    @done = true
    @fiber = nil
  end

  self
end

Instance Method Details

#current ⇒ Object

Returns the element at the current position.



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# File 'lib/rubysl/generator/generator.rb', line 145

def current
  if @queue.empty?
    raise EOFError, "no more elements available"
  end

  @queue.first
end

#each ⇒ Object

Rewinds the generator and enumerates the elements.



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# File 'lib/rubysl/generator/generator.rb', line 161

def each
  rewind

  until end?
    yield self.next
  end

  self
end

#end? ⇒ Boolean

Returns true if the generator has reached the end.

Returns:

  • (Boolean) 


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# File 'lib/rubysl/generator/generator.rb', line 102

def end?
  return true if @done
  return false unless @queue.empty?

  # Turn the loop over and see if we hit the end
  @fiber.resume

  return @done
end

#index ⇒ Object

Returns the current index (position) counting from zero.



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# File 'lib/rubysl/generator/generator.rb', line 118

def index
  @index
end

#next ⇒ Object

Returns the element at the current position and moves forward.

Raises:

  • (EOFError) 


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# File 'lib/rubysl/generator/generator.rb', line 128

def next
  raise EOFError, "end of iteration hit" if end?

  @fiber.resume if @queue.empty?

  # We've driven the fiber ahead and least once now, so we should
  # have values if there are values to be had

  unless @queue.empty?
    @index += 1
    return @queue.shift
  end

  raise EOFError, "end of iteration hit"
end

#next? ⇒ Boolean

Returns true if the generator has not reached the end yet.

Returns:

  • (Boolean) 


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# File 'lib/rubysl/generator/generator.rb', line 113

def next?
  !end?
end

#pos ⇒ Object

Returns the current index (position) counting from zero.



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# File 'lib/rubysl/generator/generator.rb', line 123

def pos
  @index
end

#rewind ⇒ Object

Rewinds the generator.



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# File 'lib/rubysl/generator/generator.rb', line 154

def rewind
  initialize(nil, &@block) if @index.nonzero?

  self
end

#yield(value) ⇒ Object

Yields an element to the generator.



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# File 'lib/rubysl/generator/generator.rb', line 93

def yield(value)
  # Running inside @fiber
  @queue << value
  Rubinius::Fiber.yield

  self
end