to_enum(*args) public

Creates a new Enumerator which will enumerate by calling method on obj, passing args if any.

If a block is given, it will be used to calculate the size of the enumerator without the need to iterate it (see Enumerator#size).


str = "xyz"

enum = str.enum_for(:each_byte)
enum.each { |b| puts b }
# => 120
# => 121
# => 122

# protect an array from being modified by some_method
a = [1, 2, 3]

It is typical to call to_enum when defining methods for a generic Enumerable, in case no block is passed.

Here is such an example, with parameter passing and a sizing block:

module Enumerable
  # a generic method to repeat the values of any enumerable
  def repeat(n)
    raise ArgumentError, "#{n} is negative!" if n < 0
    unless block_given?
      return to_enum(__method__, n) do # __method__ is :repeat here
        sz = size     # Call size and multiply by n...
        sz * n if sz  # but return nil if size itself is nil
    each do |*val|
      n.times { yield *val }

%i[hello world].repeat(2) { |w| puts w }
  # => Prints 'hello', 'hello', 'world', 'world'
enum = (1..14).repeat(3)
  # => returns an Enumerator when called without a block
enum.first(4) # => [1, 1, 1, 2]
enum.size # => 42
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August 23, 2008
2 thanks

Needs requiring 'enumerator' to work

This method needs that you

require 'enumerator'

for this method to be available.

July 30, 2011 - (>= v1_9_1_378)
0 thanks

now they are built-in

in ruby 1.9 and afterwards, the to_enum and enum_for(synonym for to_enum) methods are buil-in to the language. so there’s no need to require that any more.