Range

A Range object represents a collection of values that are between given begin and end values.

You can create an Range object explicitly with:

• A range literal:

  Example

  Run in Playground

  # Ranges that use '..' to include the given end value.
  (1..4).to_a      # => [1, 2, 3, 4]
  ('a'..'d').to_a  # => ["a", "b", "c", "d"]
  # Ranges that use '...' to exclude the given end value.
  (1...4).to_a     # => [1, 2, 3]
  ('a'...'d').to_a # => ["a", "b", "c"]
  

A range may be created using method Range.new:

# Ranges that by default include the given end value.
Range.new(1, 4).to_a     # => [1, 2, 3, 4]
Range.new('a', 'd').to_a # => ["a", "b", "c", "d"]
# Ranges that use third argument +exclude_end+ to exclude the given end value.
Range.new(1, 4, true).to_a     # => [1, 2, 3]
Range.new('a', 'd', true).to_a # => ["a", "b", "c"]

Beginless Ranges

A beginless range has a definite end value, but a nil begin value. Such a range includes all values up to the end value.

r = (..4)               # => nil..4
r.begin                 # => nil
r.include?(-50)         # => true
r.include?(4)           # => true

r = (...4)              # => nil...4
r.include?(4)           # => false

Range.new(nil, 4)       # => nil..4
Range.new(nil, 4, true) # => nil...4

A beginless range may be used to slice an array:

a = [1, 2, 3, 4]
r = (..2) # => nil...2
a[r]      # => [1, 2]

Method each for a beginless range raises an exception.

Endless Ranges

An endless range has a definite begin value, but a nil end value. Such a range includes all values from the begin value.

r = (1..)         # => 1..
r.end             # => nil
r.include?(50)    # => true

Range.new(1, nil) # => 1..

The literal for an endless range may be written with either two dots or three. The range has the same elements, either way. But note that the two are not equal:

r0 = (1..)           # => 1..
r1 = (1...)          # => 1...
r0.begin == r1.begin # => true
r0.end == r1.end     # => true
r0 == r1             # => false

An endless range may be used to slice an array:

a = [1, 2, 3, 4]
r = (2..) # => 2..
a[r]      # => [3, 4]

Method each for an endless range calls the given block indefinitely:

a = []
r = (1..)
r.each do |i|
  a.push(i) if i.even?
  break if i > 10
end
a # => [2, 4, 6, 8, 10]

Ranges and Other Classes

An object may be put into a range if its class implements instance method <=>. Ruby core classes that do so include Array, Complex, File::Stat, Float, Integer, Kernel, Module, Numeric, Rational, String, Symbol, and Time.

Example:

t0 = Time.now         # => 2021-09-19 09:22:48.4854986 -0500
t1 = Time.now         # => 2021-09-19 09:22:56.0365079 -0500
t2 = Time.now         # => 2021-09-19 09:23:08.5263283 -0500
(t0..t2).include?(t1) # => true
(t0..t1).include?(t2) # => false

A range can be iterated over only if its elements implement instance method succ. Ruby core classes that do so include Integer, String, and Symbol (but not the other classes mentioned above).

Iterator methods include:

• In Range itself: each, step, and %

• Included from module Enumerable: each_entry, each_with_index, each_with_object, each_slice, each_cons, and reverse_each.

Example:

a = []
(1..4).each {|i| a.push(i) }
a # => [1, 2, 3, 4]

Ranges and User-Defined Classes

A user-defined class that is to be used in a range must implement instance <=>; see Integer#<=>. To make iteration available, it must also implement instance method succ; see Integer#succ.

The class below implements both <=> and succ, and so can be used both to construct ranges and to iterate over them. Note that the Comparable module is included so the == method is defined in terms of <=>.

# Represent a string of 'X' characters.
class Xs
  include Comparable
  attr_accessor :length
  def initialize(n)
    @length = n
  end
  def succ
    Xs.new(@length + 1)
  end
  def <=>(other)
    @length <=> other.length
  end
  def to_s
    sprintf "%2d #{inspect}", @length
  end
  def inspect
    'X' * @length
  end
end

r = Xs.new(3)..Xs.new(6) #=> XXX..XXXXXX
r.to_a                   #=> [XXX, XXXX, XXXXX, XXXXXX]
r.include?(Xs.new(5))    #=> true
r.include?(Xs.new(7))    #=> false

What’s Here

First, what’s elsewhere. Class Range:

• Inherits from class Object.

• Includes module Enumerable, which provides dozens of additional methods.

Here, class Range provides methods that are useful for:

• Creating a Range

• Querying

• Comparing

• Iterating

• Converting

Methods for Creating a Range

• ::new

  Returns a new range.

Methods for Querying

• begin

  Returns the begin value given for self.

• bsearch

  Returns an element from self selected by a binary search.

• count

  Returns a count of elements in self.

• end

  Returns the end value given for self.

• exclude_end?

  Returns whether the end object is excluded.

• first

  Returns the first elements of self.

• hash

  Returns the integer hash code.

• last

  Returns the last elements of self.

• max

  Returns the maximum values in self.

• min

  Returns the minimum values in self.

• minmax

  Returns the minimum and maximum values in self.

• size

  Returns the count of elements in self.

Methods for Comparing

• #==

  Returns whether a given object is equal to self (uses ==).

• ===

  Returns whether the given object is between the begin and end values.

• cover?

  Returns whether a given object is within self.

• eql?

  Returns whether a given object is equal to self (uses eql?).

• include? (aliased as member?)

  Returns whether a given object is an element of self.

Methods for Iterating

• %

  Requires argument n; calls the block with each n-th element of self.

• each

  Calls the block with each element of self.

• step

  Takes optional argument n (defaults to 1); calls the block with each n-th element of self.

Methods for Converting

• inspect

  Returns a string representation of self (uses inspect).

• to_a (aliased as entries)

  Returns elements of self in an array.

• to_s

  Returns a string representation of self (uses to_s).