What is this &:last Ruby construct called? [duplicate]

by

This is shorthand for:

survey.map { |s| s.questions }.flatten.compact

It’s the Symbol#to_proc method. It used to be a part of Rails’ ActiveSupport, but has since been added to Ruby syntax.

As far as performance goes, I wrote a quick benchmark script to get an idea of performance effect in both 1.8 and 1.9.

require 'benchmark'

many = 500
a = (1..10000).to_a

Benchmark.bm do |x|
  x.report('block once') { a.map { |n| n.to_s } }
  x.report('to_proc once') { a.map(&:to_s) }
  x.report('block many') { many.times { a.map { |n| n.to_s } } }
  x.report('to_proc many') { many.times { a.map(&:to_s) } }
end

First off, before giving you the results – if you weren’t already sure that Ruby 1.9 was a huge speed improvement in general, prepare to be blown away.

Ruby 1.8 results:

                user        system      total       real
block once      0.020000    0.000000    0.020000    (  0.016781)
to_proc once    0.010000    0.000000    0.010000    (  0.013881)
block many      6.680000    1.100000    7.780000    (  7.780532)
to_proc many    7.370000    0.540000    7.910000    (  7.902935)

Ruby 1.9 results:

                user        system      total       real
block once      0.010000    0.000000    0.010000    (  0.011433)
to_proc once    0.000000    0.000000    0.000000    (  0.004929)
block many      4.060000    0.000000    4.060000    (  4.057013)
to_proc many    2.810000    0.000000    2.810000    (  2.810312)

First off: Wow. Ruby 1.9 is fast. But the more relevant conclusions we draw here are interesting:

  • In both cases, for only one run, to_proc is clearly faster. In 1.8 on the many-times run, it’s tad slower. This seems to indicate that the only real performance bottleneck is creating all those Proc objects.
  • In Ruby 1.9, however, the to_proc method is clearly much faster than blocks, no matter how many times you do it. In this case, you not only get cleaner code, but improved performance, as well.

In the end, no matter which version you’re using, to_proc is clearly not enough of a performance issue to be worth not using – in fact, it sometimes speeds things up!

More Related Contents:

  1. What is Ruby’s double-colon `::`?
  2. Using do block vs braces {}
  3. How to generate a random string in Ruby
  4. Code block passed to each works with brackets but not with ‘do’-‘end’ (ruby)
  5. Array#each vs. Array#map
  6. Trying to learn / understand Ruby setter and getter methods
  7. How do I copy a hash in Ruby?
  8. Is there a “do … while” loop in Ruby?
  9. what is the functionality of “&: ” operator in ruby? [duplicate]
  10. Find indices of elements that match a given condition
  11. How do I remove emoji from string
  12. Ruby multidimensional array
  13. Failed to build gem native extension (installing Compass)
  14. Why do I get a “permission denied” error while installing a gem?
  15. How do I keep the delimiters when splitting a Ruby string?
  16. How do you downgrade rubygems?
  17. How to search a folder and all of its subfolders for files of a certain type
  18. Why are gems installed in a directory with a different Ruby version than I’m running?
  19. Shortcut to make case/switch return a value
  20. What is a regex to match a string NOT at the end of a line?
  21. Can Ruby print out time difference (duration) readily?
  22. How do I format a date in ruby to include “rd” as in “3rd”
  23. When do Ruby instance variables get set?
  24. Is order of a Ruby hash literal guaranteed?
  25. RVM and thin, root vs. local user
  26. Ruby array subtraction without removing items more than once
  27. Where is it legal to use ruby splat operator?
  28. Net::ReadTimeout (Net::ReadTimeout) Selenium Ruby
  29. Rails ‘parse_query’ error on server in brand new app
  30. How do I remove blank elements from an array?

Leave a Comment