Notes posted by Rubybull

How does enum#each_index differ from enum#with_each_index ?

Here is the working one each_with__index:

a=[11,22,31,224,44].each_with_index { |val,index| puts "index: #{index} for #{val}" if val < 30}
  index: 0 for 11
  index: 1 for 22
  => [11, 22, 31, 224, 44]

Below couldn’t produce the output, as with_index couldn’t work on the array.To make it workble, we need to first convert it to enumerator. And that can be done via the help of .to_enum, .each, or .map

a = [11,22,31,224,44].with_index { |val,index| puts "index: #{index} for #{val}" if val < 30}
=>NoMethodError: undefined method `with_index' for [11, 22, 31, 224, 44]:Array
       from (irb):2
       from C:/Ruby193/bin/irb:12:in `<main>'

Here is the working one with_index:

a = [11,22,31,224,44].each.with_index { |val,index| puts "index: #{index} for #{val}" if val < 30}
index: 0 for 11
index: 1 for 22
=> [11, 22, 31, 224, 44]

Difference between enum#with_object and enum#each_with_object

I found a very good post on SO - which clearly explained the difference between enum#with_object and enum#each_with_object. The link is as follows:

http://stackoverflow.com/questions/14671881/how-does-enumwith-object-differ-from-enumeach-with-object/14672305#14672305

Enumerator#with_index has confusing documentation

Enumerator#with_index has confusing documentation, but hopefully this will make it clearer.

Code example

a=[11,22,31,224,44].to_enum
=> [11, 22, 31, 224, 44]
a.with_index { |val,index| puts "index: #{index} for #{val}" }
index: 0 for 11
index: 1 for 22
index: 2 for 31
index: 3 for 224
index: 4 for 44

a=[11,22,31,224,44].to_enum
=> #<Enumerator: [11, 22, 31, 224, 44]:each>
a.with_index(2){ |val,index| puts "index: #{index} for #{val}" if val > 30 }
index: 4 for 31
index: 5 for 224
index: 6 for 44
=> [11, 22, 31, 224, 44