Class: Enumerator

Inherits:
Object
  • Object
show all
Includes:
Enumerable
Defined in:
mrbgems/mruby-enumerator/mrblib/enumerator.rb,
mrbgems/mruby-enum-lazy/mrblib/lazy.rb,
mrbgems/mruby-enum-chain/mrblib/chain.rb

Overview

A class which allows both internal and external iteration.

An Enumerator can be created by the following methods.

Most methods have two forms: a block form where the contents are evaluated for each item in the enumeration, and a non-block form which returns a new Enumerator wrapping the iteration.

  enumerator = %w(one two three).each
  puts enumerator.class # => Enumerator

  enumerator.each_with_object("foo") do |item, obj|
    puts "#{obj}: #{item}"
  end

  # foo: one
  # foo: two
  # foo: three

  enum_with_obj = enumerator.each_with_object("foo")
  puts enum_with_obj.class # => Enumerator

  enum_with_obj.each do |item, obj|
    puts "#{obj}: #{item}"
  end

  # foo: one
  # foo: two
  # foo: three

This allows you to chain Enumerators together. For example, you can map a list's elements to strings containing the index and the element as a string via:

  puts %w[foo bar baz].map.with_index { |w, i| "#{i}:#{w}" }
  # => ["0:foo", "1:bar", "2:baz"]

An Enumerator can also be used as an external iterator. For example, Enumerator#next returns the next value of the iterator or raises StopIteration if the Enumerator is at the end.

  e = [1,2,3].each   # returns an enumerator object.
  puts e.next   # => 1
  puts e.next   # => 2
  puts e.next   # => 3
  puts e.next   # raises StopIteration

You can use this to implement an internal iterator as follows:

  def ext_each(e)
    while true
      begin
        vs = e.next_values
      rescue StopIteration
        return $!.result
      end
      y = yield(*vs)
      e.feed y
    end
  end

  o = Object.new

  def o.each
    puts yield
    puts yield(1)
    puts yield(1, 2)
    3
  end

  # use o.each as an internal iterator directly.
  puts o.each {|*x| puts x; [:b, *x] }
  # => [], [:b], [1], [:b, 1], [1, 2], [:b, 1, 2], 3

  # convert o.each to an external iterator for
  # implementing an internal iterator.
  puts ext_each(o.to_enum) {|*x| puts x; [:b, *x] }
  # => [], [:b], [1], [:b, 1], [1, 2], [:b, 1, 2], 3

Direct Known Subclasses

Lazy

Defined Under Namespace

Classes: Chain, Generator, Lazy, Yielder

Constant Summary

Constants included from Enumerable

Enumerable::NONE

Instance Method Summary collapse

Methods included from Enumerable

#all?, #any?, #chain, #chunk, #chunk_while, #collect, #count, #cycle, #detect, #drop, #drop_while, #each_cons, #each_entry, #each_slice, #each_with_object, #entries, #filter_map, #find_all, #find_index, #first, #flat_map, #grep, #grep_v, #group_by, #hash, #include?, #inject, #lazy, #max, #max_by, #min, #min_by, #minmax, #minmax_by, #none?, #one?, #partition, #reject, #reverse_each, #sort, #sort_by, #sum, #take, #take_while, #tally, #to_h, #uniq, #zip

Constructor Details

#initialize(obj, method = :each, *args, **kwd) ⇒ Enumerator

Creates a new Enumerator object, which can be used as an Enumerable.

In the first form, iteration is defined by the given block, in which a "yielder" object, given as block parameter, can be used to yield a value by calling the yield method (aliased as <<):

fib = Enumerator.new do |y|
  a = b = 1
  loop do
    y << a
    a, b = b, a + b
  end
end

p fib.take(10) # => [1, 1, 2, 3, 5, 8, 13, 21, 34, 55]

In the second, deprecated, form, a generated Enumerator iterates over the given object using the given method with the given arguments passed. This form is left only for internal use.

Use of this form is discouraged. Use Kernel#enum_for or Kernel#to_enum instead.



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# File 'mrbgems/mruby-enumerator/mrblib/enumerator.rb', line 117

def initialize(obj=NONE, meth=:each, *args, **kwd, &block)
  if block
    obj = Generator.new(&block)
  elsif NONE.equal?(obj)
    raise ArgumentError, "wrong number of arguments (given 0, expected 1+)"
  end

  @obj = obj
  @meth = meth
  @args = args
  @kwd = kwd
  @fib = nil
  @dst = nil
  @lookahead = nil
  @feedvalue = nil
  @stop_exc = false
end

Instance Method Details

#+(other) ⇒ Object

call-seq:

enum + other_enum -> enumerator_chain

Returns an Enumerator::Chain object which can enumerate over this enumerator and the given enumerator in sequence.

e1 = (1..3).each
e2 = [4, 5].each
(e1 + e2).to_a  #=> [1, 2, 3, 4, 5]


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# File 'mrbgems/mruby-enum-chain/mrblib/chain.rb', line 33

def +(other)
  Chain.new(self, other)
end

#each(*argv, &block) ⇒ Object

call-seq:

enum.each { |elm| block }                    -> obj
enum.each                                    -> enum
enum.each(*appending_args) { |elm| block }   -> obj
enum.each(*appending_args)                   -> an_enumerator

Iterates over the block according to how this Enumerator was constructed. If no block and no arguments are given, returns self.

Examples

Array.new(3)                     #=> [nil, nil, nil]
Array.new(3) { |i| i }           #=> [0, 1, 2]
Array.to_enum(:new, 3).to_a      #=> [0, 1, 2]
Array.to_enum(:new).each(3).to_a #=> [0, 1, 2]

obj = Object.new

def obj.each_arg(a, b=:b, *rest)
yield a
yield b
yield rest
:method_returned
end

enum = obj.to_enum :each_arg, :a, :x

enum.each.to_a                  #=> [:a, :x, []]
enum.each.equal?(enum)          #=> true
enum.each { |elm| elm }         #=> :method_returned

enum.each(:y, :z).to_a          #=> [:a, :x, [:y, :z]]
enum.each(:y, :z).equal?(enum)  #=> false
enum.each(:y, :z) { |elm| elm } #=> :method_returned


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# File 'mrbgems/mruby-enumerator/mrblib/enumerator.rb', line 304

def each(*argv, &block)
  obj = self
  if 0 < argv.length
    obj = self.dup
    args = obj.instance_eval{@args}
    if !args.empty?
      args = args.dup
      args.concat argv
    else
      args = argv.dup
    end
    obj.instance_eval{@args = args}
  end
  return obj unless block
  __enumerator_block_call(&block)
end

#each_with_index(&block) ⇒ Object

call-seq:

e.each_with_index {|(*args), idx| ... }
e.each_with_index

Same as Enumerator#with_index(0), i.e. there is no starting offset.

If no block is given, a new Enumerator is returned that includes the index.



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# File 'mrbgems/mruby-enumerator/mrblib/enumerator.rb', line 191

def each_with_index(&block)
  with_index(0, &block)
end

#feed(value) ⇒ Object

call-seq:

e.feed obj   -> nil

Sets the value to be returned by the next yield inside e.

If the value is not set, the yield returns nil.

This value is cleared after being yielded.

# Array#map passes the array's elements to "yield" and collects the
# results of "yield" as an array.
# Following example shows that "next" returns the passed elements and
# values passed to "feed" are collected as an array which can be
# obtained by StopIteration#result.
e = [1,2,3].map
p e.next           #=> 1
e.feed "a"
p e.next           #=> 2
e.feed "b"
p e.next           #=> 3
e.feed "c"
begin
e.next
rescue StopIteration
p $!.result      #=> ["a", "b", "c"]
end

o = Object.new
def o.each
x = yield         # (2) blocks
p x               # (5) => "foo"
x = yield         # (6) blocks
p x               # (8) => nil
x = yield         # (9) blocks
p x               # not reached w/o another e.next
end

e = o.to_enum
e.next              # (1)
e.feed "foo"        # (3)
e.next              # (4)
e.next              # (7)
                  # (10)

Raises:

  • (TypeError) 


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# File 'mrbgems/mruby-enumerator/mrblib/enumerator.rb', line 554

def feed(value)
  raise TypeError, "feed value already set" if @feedvalue
  @feedvalue = value
  nil
end

#inspect ⇒ Object

call-seq:

enum.inspect -> string

Returns a string representation of the enumerator.

[1, 2, 3].each.inspect  #=> "#<Enumerator: [1, 2, 3]:each>"
[1, 2, 3].map.inspect   #=> "#<Enumerator: [1, 2, 3]:map>"


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# File 'mrbgems/mruby-enumerator/mrblib/enumerator.rb', line 241

def inspect
  if @args && @args.size > 0
    args = @args.join(", ")
    "#<#{self.class}: #{@obj.inspect}:#{@meth}(#{args})>"
  else
    "#<#{self.class}: #{@obj.inspect}:#{@meth}>"
  end
end

#next ⇒ Object

call-seq:

e.next   -> object

Returns the next object in the enumerator, and move the internal position forward. When the position reached at the end, StopIteration is raised.

Example

a = [1,2,3]
e = a.to_enum
p e.next   #=> 1
p e.next   #=> 2
p e.next   #=> 3
p e.next   #raises StopIteration

Note that enumeration sequence by next does not affect other non-external enumeration methods, unless the underlying iteration methods itself has side-effect



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# File 'mrbgems/mruby-enumerator/mrblib/enumerator.rb', line 346

def next
  next_values.__svalue
end

#next_values ⇒ Object

call-seq:

e.next_values   -> array

Returns the next object as an array in the enumerator, and move the internal position forward. When the position reached at the end, StopIteration is raised.

This method can be used to distinguish yield and yield nil.

Example

o = Object.new
def o.each
yield
yield 1
yield 1, 2
yield nil
yield [1, 2]
end
e = o.to_enum
p e.next_values
p e.next_values
p e.next_values
p e.next_values
p e.next_values
e = o.to_enum
p e.next
p e.next
p e.next
p e.next
p e.next

## yield args       next_values      next
#  yield            []               nil
#  yield 1          [1]              1
#  yield 1, 2       [1, 2]           [1, 2]
#  yield nil        [nil]            nil
#  yield [1, 2]     [[1, 2]]         [1, 2]

Note that next_values does not affect other non-external enumeration methods unless underlying iteration method itself has side-effect

Raises:

  • (@stop_exc) 


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# File 'mrbgems/mruby-enumerator/mrblib/enumerator.rb', line 394

def next_values
  if @lookahead
    vs = @lookahead
    @lookahead = nil
    return vs
  end
  raise @stop_exc if @stop_exc

  curr = Fiber.current

  if !@fib || !@fib.alive?
    @dst = curr
    @fib = Fiber.new do
      result = each do |*args|
        feedvalue = nil
        Fiber.yield args
        if @feedvalue
          feedvalue = @feedvalue
          @feedvalue = nil
        end
        feedvalue
      end
      @stop_exc = StopIteration.new "iteration reached an end"
      @stop_exc.result = result
      Fiber.yield nil
    end
    @lookahead = nil
  end

  vs = @fib.resume curr
  if @stop_exc
    @fib = nil
    @dst = nil
    @lookahead = nil
    @feedvalue = nil
    raise @stop_exc
  end
  vs
end

#peek ⇒ Object

call-seq:

e.peek   -> object

Returns the next object in the enumerator, but doesn't move the internal position forward. If the position is already at the end, StopIteration is raised.

Example

a = [1,2,3]
e = a.to_enum
p e.next   #=> 1
p e.peek   #=> 2
p e.peek   #=> 2
p e.peek   #=> 2
p e.next   #=> 2
p e.next   #=> 3
p e.next   #raises StopIteration


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# File 'mrbgems/mruby-enumerator/mrblib/enumerator.rb', line 454

def peek
  peek_values.__svalue
end

#peek_values ⇒ Object

call-seq:

e.peek_values   -> array

Returns the next object as an array, similar to Enumerator#next_values, but doesn't move the internal position forward. If the position is already at the end, StopIteration is raised.

Example

o = Object.new
def o.each
yield
yield 1
yield 1, 2
end
e = o.to_enum
p e.peek_values    #=> []
e.next
p e.peek_values    #=> [1]
p e.peek_values    #=> [1]
e.next
p e.peek_values    #=> [1, 2]
e.next
p e.peek_values    # raises StopIteration


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# File 'mrbgems/mruby-enumerator/mrblib/enumerator.rb', line 484

def peek_values
  if @lookahead.nil?
    @lookahead = next_values
  end
  @lookahead.dup
end

#rewind ⇒ Object

call-seq:

e.rewind   -> e

Rewinds the enumeration sequence to the beginning.

If the enclosed object responds to a "rewind" method, it is called.



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# File 'mrbgems/mruby-enumerator/mrblib/enumerator.rb', line 499

def rewind
  @obj.rewind if @obj.respond_to? :rewind
  @fib = nil
  @dst = nil
  @lookahead = nil
  @feedvalue = nil
  @stop_exc = false
  self
end

#size ⇒ Object

call-seq:

enum.size -> int, float, or nil

Returns the size of the enumerator, or nil if it cannot be calculated lazily.

[1, 2, 3].each.size    #=> 3
(1..100).each.size     #=> 100
loop.size              #=> nil


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# File 'mrbgems/mruby-enumerator/mrblib/enumerator.rb', line 260

def size
  if @size
    @size
  elsif @obj.respond_to?(:size)
    @obj.size
  end
end

#with_index(offset = 0, &block) ⇒ Object

call-seq:

e.with_index(offset = 0) {|(*args), idx| ... }
e.with_index(offset = 0)

Iterates the given block for each element with an index, which starts from offset. If no block is given, returns a new Enumerator that includes the index, starting from offset

offset

the starting index to use



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# File 'mrbgems/mruby-enumerator/mrblib/enumerator.rb', line 166

def with_index(offset=0, &block)
  return to_enum(:with_index, offset) unless block

  if offset.nil?
    offset = 0
  else
    offset = offset.__to_int
  end

  n = offset - 1
  __enumerator_block_call do |*i|
    n += 1
    block.call(i.__svalue, n)
  end
end

#with_object(object, &block) ⇒ Object

call-seq:

e.each_with_object(obj) {|(*args), obj| ... }
e.each_with_object(obj)
e.with_object(obj) {|(*args), obj| ... }
e.with_object(obj)

Iterates the given block for each element with an arbitrary object, obj, and returns obj

If no block is given, returns a new Enumerator.

Examples:

to_three = Enumerator.new do |y|
  3.times do |x|
    y << x
  end
end

to_three_with_string = to_three.with_object("foo")
to_three_with_string.each do |x,string|
  puts "#{string}: #{x}"
end

# => foo:0
# => foo:1
# => foo:2


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# File 'mrbgems/mruby-enumerator/mrblib/enumerator.rb', line 223

def with_object(object, &block)
  return to_enum(:with_object, object) unless block

  __enumerator_block_call do |i|
    block.call([i,object])
  end
  object
end