Little bit ruby

% 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

Hash

nested = Hash.new { |hash, key| hash[key] = Hash.new(&hash.default_proc) }
nested[:x][:y][:z] = "value"
nested      #=> {:x=>{:y=>{:z=>"value"}}

zoo = Hash.new { |hash, key| hash[key] = 'some default value for `#{key}`' }
zoo[:foo]   #=> "some default value for `foo`"

foo = Hash.new 'some default value'
foo[:zoo]   #=> "some default value

Tap

class Foo
  attr_accessor :var
end

Foo.new.tap do |foo|
  foo.var = 'some data'
end

Lazy

range = 1..Float::INFINITY      #=> 1..Infinity
range.map { |x| x+x }.first(10) #=> infinite loop
range.lazy.map { |x| x+x }.first(10)
#=> [2, 4, 6, 8, 10, 12, 14, 16, 18, 20]

Wrap method

(1..5).each &method(:puts)
method(:puts)["args"] #=> "args"

Struct

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

struct = Struct::Tuple.new('left', 'right')
struct.pair #=> "(left, right)"

Merge trick

a = {a: 1, b: 2, c: 3}
b = {a: 3, b: 2, c: 1}

a.merge(b) {|key, first, second| first + second }
#=> {a: 4, b: 4, c: 4}

Get method location

self.method(:highlight).source_location