Ruby 2.7 adds Beginless Range

Ruby 2.7 added support for Beginless Range which makes the start of range an optional parameter.

(..100) is a Beginless Range and it is equivalent to (nil..100).

Let's see how Beginless Range could be used.

1> array = (1..10).to_a
2
3# Select first 6 elements
4> array[..5]
5=> [1, 2, 3, 4, 5, 6]
6
7# Select first 5 elements
8> array[...5]
9=> [1, 2, 3, 4, 5]
10
11# grep (INFINITY..5) in (1..5)
12> (1..10).grep(..5)
13=> [1, 2, 3, 4, 5]
14
15# (..100) is equivalent to (nil..100)
16> (..100) == (nil..100)
17=> true
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Here is another example where in the case statement the condition can be read as below the specified level.

1case temperature
2when ..-15
3  puts "Deep Freeze"
4when -15..8
5  puts "Refrigerator"
6when 8..15
7  puts "Cold"
8when 15..25
9  puts "Room Temperature"
10when (25..)   # Kindly notice the brackets here
11  puts "Hot"
12end
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It can also be used for defining constants for ranges.

1TEMPERATURE = {
2  ..-15  => :deep_freeze,
3  -15..8 => :refrigerator,
4  8..15  => :cold,
5  15..25 => :room_temperature,
6  25..   => :hot
7end
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Using Beginless Range in DSL makes it easier to write conditions and it looks more natural.

1
2# In Rails
3User.where(created_at: (..DateTime.now))
4# User Load (2.2ms)  SELECT "users".* FROM "users" WHERE "users"."created_at" <= $1 LIMIT $2  [["created_at", "2020-08-05 15:00:19.111217"], ["LIMIT", 11]]
5
6
7# In RubySpec
8ruby_version(..'1.9') do
9# Tests for old Ruby
10end
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Here is the relevant commit and discussion regarding this change.