Creates numbers quickly

[*1..10]

# other way around

10.step(by: -1, to: 0).to_a

Sort Reversely

[*1..10].sort_by(&:-@)

The -@ is called unary operator.

Rational and Complex Number

From Rational and Complex module.

42r # Rational(42, 1)
3.14r # 3.14.rationalize

42i # Complex(0, 42)
3.14i # Complex(0, 3.14)

3r + 4i

Since Ruby 2.1.

Function Compositions

<< and >> from Ruby 2.6.0.

plus_two = proc { |x| x + 2 }
three_times = proc { |x| x * 3 }
(plus_two << three_times).call(3) # plus_two(three_times(3))
(plus_two >> three_times).call(3) # three_times(plus_two(3))

Initialize Struct with keyword arguments

User = Struct.new(:name, :handle, keyword_init: true)
User.new(name: "Juanito Fatas", handle: "JuanitoFatas")

Since Ruby 2.5: Feature#11925.

Endless Range

array[1..]
(1..).each {|i| puts i }

Since Ruby 2.6: Feature#12912

Beginless Range

array[..42]
(..42).each {|i| puts i }

Since Ruby 2.7.

Count number of elements in array

["a", "b", "c", "b"].tally
#=> {"a"=>1, "b"=>2, "c"=>1}

Since Ruby 2.7.

Delegate arguments

def parent_method(...)
  child_method(...)
end

instead of

def parent_method(*args, **options, &block)
  child_method(*args, **options, &block)
end

Since Ruby 2.7: Feature#16253.