enum_for(*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).
Examples
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] some_method(a.to_enum)
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 end end each do |*val| n.times { yield *val } end end end %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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yonosoytu -
August 23, 2008
4 thanks
Needs requiring 'enumerator' to work
This method needs that you
require 'enumerator'
for this method to be available.
rob-twf -
May 27, 2009 - (>= v1_8_6_287)
3 thanks
map_with_index
If you want to access the element index when using map, you can do it with enum_for:
(1..6).enum_for(:each_with_index).map { |v, i| "index: #{i} value: #{v}" } #=> ["index: 0 value: 1", "index: 1 value: 2", "index: 2 value: 3", "index: 3 value: 4", "index: 4 value: 5", "index: 5 value: 6"]