What do you call the &: operator in Ruby? [duplicate]

by

There’s a few moving pieces here, but the name for what’s going on is the Symbol#to_proc conversion. This is part of Ruby 1.9 and up, and is also available if you use later-ish versions of Rails.

First, in Ruby, :foo means “the symbol foo“, so it’s actually two separate operators you’re looking at, not one big &: operator.

When you say foo.map(&bar), you’re telling Ruby, “send a message to the foo object to invoke the map method, with a block I already defined called bar“. If bar is not already a Proc object, Ruby will try to make it one.

Here, we don’t actually pass a block, but instead a symbol called bar. Because we have an implicit to_proc conversion available on Symbol, Ruby sees that and uses it. It turns out that this conversion looks like this:

def to_proc
  proc { |obj, *args| obj.send(self, *args) }
end

This makes a proc which invokes the method with the same name as the symbol. Putting it all together, using your original example:

array.map(&:to_i)

This invokes .map on array, and for each element in the array, returns the result of calling to_i on that element.

More Related Contents:

  1. What is attr_accessor in Ruby?
  2. What is the difference between include and require in Ruby?
  3. Best practices with STDIN in Ruby? [closed]
  4. How to run Rake tasks from within Rake tasks?
  5. What is the colon operator in Ruby?
  6. Get the name of the currently executing method
  7. Ruby Style: How to check whether a nested hash element exists
  8. What Ruby IDE do you prefer? [closed]
  9. An easy way to support tags in a jekyll blog
  10. rhc setup gives error `no such file dl/import`
  11. Instance variable: self vs @
  12. Is it good style to explicitly return in Ruby?
  13. Get list of a class’ instance methods
  14. Comparing ruby hashes [duplicate]
  15. How can I capture STDOUT to a string?
  16. Using WWW:Mechanize to download a file to disk without loading it all in memory first
  17. What do you call the -> operator in Ruby?
  18. Understanding Ruby’s load paths
  19. Why is this RMagick call generating a segmentation fault?
  20. git, Heroku: pre-receive hook declined
  21. Understanding private methods in Ruby
  22. What is the difference between STDIN and $stdin in Ruby?
  23. Iterate through every file in one directory
  24. Why isn’t self always needed in ruby / rails / activerecord?
  25. Interpolating a string into a regex
  26. Ruby: Installing rmagick on Ubuntu
  27. Better ruby markdown interpreter?
  28. How to understand the difference between class_eval() and instance_eval()?
  29. Understanding Ruby and OS I/O buffering
  30. Rake “already initialized constant WFKV_” warning

Leave a Comment