Hidden features of Ruby you may not know about

How well do you know the language you're using? What if I tell you that even you use it the whole day and every day it still can hide some tricks that you might not be aware of? I'd like to reveal some less or more known, but certainly interesting parts of Ruby to make you sure that you don't miss anything.

Disclaimer

Every example was run with:

→ ruby -v
ruby 2.1.2p95 (2014-05-08 revision 45877) [x86_64-darwin13.0]
and

→ pry -v
Pry version 0.10.0 on Ruby 2.1.2

Binary numbers

[1] pry(main)> 0b110111
=> 55

[2] pry(main)> "110111".to_i(2)
=> 55

[3] pry(main)> "%b" % 55
=> "110111"

[4] pry(main)> 55.to_s(2)
=> "110111"

Because == 0 is so mainstream

[5] pry(main)> 0 == 0
=> true

[6] pry(main)> 0.zero?
=> true

[7] pry(main)> 0.nonzero?
=> nil

[8] pry(main)> 1.nonzero?
=> 1

nonzero? returns self unless number is zero, nil otherwise.

Get some random date

require 'active_support/core_ext'
def random_birth_date_with_age_between_20_and_30
  rand(30.years.ago..20.years.ago).to_date
end

[9] pry(main)> random_birth_date_with_age_between_20_and_30
=> Sun, 21 May 1989

Call my name

def introduce1
  __method__
end

def introduce2
  __callee__
end

[10] pry(main)> introduce1
=> :introduce1

[11] pry(main)> introduce2
=> :introduce2

Hash from array(s)

Note that:

[16] pry(main)> arr.count.even?
=> true
In the other case:

[17] pry(main)> Hash[*['one', 'two', 'three']]
ArgumentError: odd number of arguments for Hash

% notation

%q[ ] # Non-interpolated String (except for \\ \[ and \])
%Q[ ] # Interpolated String (default)
%r[ ] # Interpolated Regexp (flags can appear after the closing delimiter)
%i[ ] # Non-interpolated Array of symbols, separated by whitespace
%I[ ] # Interpolated Array of symbols, separated by whitespace
%w[ ] # Non-interpolated Array of words, separated by whitespace
%W[ ] # Interpolated Array of words, separated by whitespace
%x[ ] # Interpolated shell command

Of course you can use other non-alpha-numeric character delimiters:

%[including these]
%?or these?
%~or even these things~

%w what about spaces

%(parentheses)
%[square brackets]
%{curly brackets}
%<pointy brackets>
Source and examples

'Better' errors

class MyCustomBadError < StandardError; end

MyCustomGoodError = Class.new(StandardError)

Symbol to proc

[18] pry(main)> (1..100).inject(:+)
=> 5050

[19] pry(main)> ("a".."e").map(&:upcase)
=> ["A", "B", "C", "D", "E"]

Enumerators

[20] pry(main)> enum = [1, 2, 3].each
=> #<Enumerator: ...>
[21] pry(main)> enum.next
=> 1
[22] pry(main)> enum.next
=> 2
[23] pry(main)> enum.next
=> 3
[24] pry(main)> enum.next
StopIteration: iteration reached an end
from (pry):17:in `next'

however

[25] pry(main)> enum = [1, 2, 3].cycle
=> #<Enumerator: ...>
[26] pry(main)> enum.next
=> 1
[27] pry(main)> enum.next
=> 2
[28] pry(main)> enum.next
=> 3
[29] pry(main)> enum.next
=> 1

Let's be lazy!

[30] pry(main)> range = 1..Float::INFINITY
=> 1..Infinity
[31] pry(main)> range.map { |x| x+x }.first(10)
# infinite loop

[32] pry(main)> range.lazy.map { |x| x+x }.first(10)
=> [2, 4, 6, 8, 10, 12, 14, 16, 18, 20]

Send a method

Here is nice trick to avoid tedious { |x| do_something_with(x) }. This is a different case from symbol-to-proc, because we don't invoke method on x but call a method that takes x.

[33] pry(main)> (1..5).each { |x| puts x }
1
2
3
4
5
=> 1..5

[34] pry(main)> (1..5).each &method(:puts)
1
2
3
4
5
=> 1..5

Join my array

[35] pry(main)> array = %w(this is an array)
=> ["this", "is", "an", "array"]
[36] pry(main)> array.join ', '
=> "this, is, an, array"
[37] pry(main)> array * ', '
=> "this, is, an, array"

We have a ternary operator too

def odd?(x)
  x % 2 == 0 ? 'NO' : 'YES'
end

[38] pry(main)> odd? 3
=> "YES"
[39] pry(main)> odd? 2
=> "NO"

Rescue to the defaults

[40] pry(main)> value = 1 / 0 rescue 0
=> 0

Interpolate easier

[41] pry(main)> @instance, @@class, $global = [ 'instance', 'class', 'global' ]
=> ["instance", "class", "global"]
[42] pry(main)> p "#@instance, #@@class, #$global";
instance, class, global

Wrap a method

def caller(block_or_method)
  block_or_method.call
end

def foo
  p 'foo'
end

[43] pry(main)> caller lambda { foo }
"foo"
=> "foo"
[44] pry(main)> caller -> { foo }
"foo"
=> "foo"
[45] pry(main)> caller method(:foo)
"foo"
=> "foo"

Memoization

fibbonacci = Hash.new do |accumulator, index|
  accumulator[index] = fibbonacci[index - 2] + fibbonacci[index - 1]
end.update(0 => 0, 1 => 1)

[46] pry(main)> fibbonacci[100]
=> 354224848179261915075

Tap here

class Foo
  attr_accessor :a, :b, :c
end

foo = Foo.new
foo.a = 'a'
foo.b = 'b'
foo.c = 'c'

Foo.new.tap do |foo|
  foo.a = 'a'
  foo.b = 'b'
  foo.c = 'c'
end
=> #<Foo:0x007fe1bd5f6210 @a="a", @b="b", @c="c">

Nest some stuff

[47] pry(main)> 
nested_hash = Hash.new { |hash, key| hash[key] = Hash.new(&hash.default_proc) }
=> {}
[48] pry(main)> nested_hash[:x][:y][:z] = :xyz
=> :xyz
[49] pry(main)> nested_hash
=> {:x=>{:y=>{:z=>:xyz}}}

Daemonize it

- daemon.rb
Process.daemon
loop do
  sleep
end
λ MacBook-Pro-Kamil Desktop → ruby daemon.rb
λ MacBook-Pro-Kamil Desktop → ps aux | grep daemon
   kamil 41629 0.0 0.0 2472380 472 ?? S 11:45PM 0:00.00 ruby daemon.rb

Candy shop

require 'yaml/store'
store = YAML::Store.new 'candy.yml'

store.transaction do
  store['candy']    = "m&m's"
  store['lollipop'] = 'Chupa Chups'
end

store.transaction do
  store.abort # you can resign from buying
end

store.transaction do
  p store['candy']    # "m&m's"
  p store['lollipop'] # 'Chupa Chups'
end

Struct on

Struct.new('Tuple', :first, :second) do
  def pair
    "(#{first}, #{second})"
  end
end

[50] pry(main)> struct = Struct::Tuple.new('left', 'right')
=> #<struct Struct::Tuple first="left", second="right">
[51] pry(main)> struct.pair
=> "(left, right)"

Have some defaults

[52] pry(main)> zoo = Hash.new { |hash, key| hash[key] = 0 }
=> {}
[53] pry(main)> zoo.fetch :gorillas, 0
=> 0
[54] pry(main)> zoo.fetch :gorillas
=> 0
[55] pry(main)> zoo[:gorillas]
=> 0

And many more.

Painless arrays

array of size 3 containing only 0s [56] pry(main)> Array.new(3, 0) => [0, 0, 0]
choose random number and "replicate" it 3 times [57] pry(main)> Array.new(3, rand(10)) => [8, 8, 8]
build array of size 3 with random number on each index [58] pry(main)> Array.new(3) { rand(100) } => [17, 99, 72]

Play with URLs

require 'uri'

[59] pry(main)> URI::HTTP.build(['kamil', 'arkency.com', 8080, '/path', 'query', 'fragment'])
=> #<URI::HTTP:0x007f8efd43a150 URL:http://[email protected]:8080/path?query#fragment>

require 'active_support/core_ext/object/to_query'

[60] pry(main)> 
"http://www.arkency.com?" + { language: "ruby", status: "professional" }.to_query
=> "http://www.arkency.com?language=ruby&status=professional"

require 'cgi'
[61] pry(main)> CGI::parse "language=ruby&status=awesome"
=> {"language"=>["ruby"], "status"=>["awesome"]}

Access the hash

require 'active_support/core_ext/hash/indifferent_access'

[62] pry(main)> 
rgb = { black: '#000000', white: '#FFFFFF' }.with_indifferent_access
=> {"black"=>"#000000", "white"=>"#FFFFFF"}
[63] pry(main)> rgb[:black]
=> "#000000"
[64] pry(main)> rgb['black']
=> "#000000"

Expand range

[65] pry(main)> p *(1..5)
1
2
3
4
5
=> [1, 2, 3, 4, 5]

[66] pry(main)> [*('a'..'e')]
 => ["a", "b", "c", "d", "e"]

[67] pry(main)> numbers = *('00'..'10')
 => ["00", "01", "02", "03", "04", "05", "06", "07", "08", "09", "10"]

Summary

Impressed? If no, that's great! It means you are a trouper. Otherwise, it's good too, because you learned something new today and I hope you find this useful.

vicmaster/hidden_features_of_ruby.md