Ampersand tricks in Ruby

1_simple_to_proc.rb

#!/usr/bin/env ruby
# Modify all values of an array the same way

# Do you often see code like this?
puts [0.3, 0.5, 0.7].map{|float| float.round} # [0, 1, 1]

# We can do better!
puts [0.3, 0.5, 0.7].map(&:round) # [0, 1, 1]

2_advanced_to_proc.rb

#!/usr/bin/env ruby
# Wanna sum up the content of an array?

# You have experience in traditional for-loops?
sum = 0
for value in [1, 2, 3]
  sum += value
end
puts sum # 6

# You are just a Ruby beginner and start liking #each?
sum = 0
[1, 2, 3].each{|value| sum += value} 
puts sum # 6

# You've heard about #inject?
puts [1, 2, 3].inject(0){|sum, value| sum += value} # 6

# Oh, come on!
puts [1, 2, 3].inject(&:+) # 6

3_custom_to_proc.rb

#!/usr/bin/env ruby
# Wanna make some predictions?

class ExEarthNewsReporter
  def publish location, mission, year
    puts "The first manned #{location} landing was in #{year} (#{mission})."
  end

  # Here is the magic!
  def to_proc
    Proc.new { |args| self.publish *args; nil}
  end
end

[["moon", "Apollo 11", 1969],
 ["mars", "Mars One", 2023]].each(&ExEarthNewsReporter.new)

4_method_and_to_proc.rb

#!/usr/bin/env ruby
# subject <=> object

["Is it any good?", " - Yes."].map(&method(:puts))