What is Enumerator object? (Created with String#gsub)

Question

I have an attributes array as follows,

attributes = ["test, 2011", "photo", "198.1 x 198.1 cm", "Photo: Manu PK Full Screen"]

When i do this,

artist = attributes[-1].gsub("Photo:")
p artist

i get the following output in terminal

#<Enumerator: "Photo: Manu PK Full Screen":gsub("Photo:")>

Wondering why am I getting an enumerator object as output? Thanks in advance.

EDIT: Please note that instead of attributes[-1].gsub("Photo:", ""), I am doing attributes[-1].gsub("Photo:") So would like to know why enumerator object has returned here( I was expecting an error message) and what is going on.?

Ruby - 1.9.2

Rails - 3.0.7

Answer 1

An Enumerator object provides some methods common to enumerations -- next, each, each_with_index, rewind, etc.

You're getting the Enumerator object here because gsub is extremely flexible:

gsub(pattern, replacement) → new_str
gsub(pattern, hash) → new_str
gsub(pattern) {|match| block } → new_str
gsub(pattern) → enumerator 

In the first three cases, the substitution can take place immediately, and return a new string. But, if you don't give a replacement string, a replacement hash, or a block for replacements, you get back the Enumerator object that lets you get to the matched pieces of the string to work with later:

irb(main):022:0> s="one two three four one"
=> "one two three four one"
irb(main):023:0> enum = s.gsub("one")
=> #<Enumerable::Enumerator:0x7f39a4754ab0>
irb(main):024:0> enum.each_with_index {|e, i| puts "#{i}: #{e}"}
0: one
1: one
=> " two three four "
irb(main):025:0>