Class: Enumerator

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

Examples

"Hello, world!".scan(/\w+/)                     #=> ["Hello", "world"]
"Hello, world!".to_enum(:scan, /\w+/).to_a      #=> ["Hello", "world"]
"Hello, world!".to_enum(:scan).each(/\w+/).to_a #=> ["Hello", "world"]

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

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

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

Alias for #with_object.

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)

Creates a printable version of e.

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, e.g. IO#each_line.

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, e.g. IO#each_line.

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.peek   #raises StopIteration

Returns the next object as an array, similar to #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

Rewinds the enumeration sequence to the beginning.

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

Returns the size of the enumerator, or nil if it can’t be calculated lazily.

(1..100).to_a.permutation(4).size # => 94109400
loop.size # => Float::INFINITY
(1..100).drop_while.size # => nil

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

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

If no block is given, returns a new Enumerator.

Example

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