Updates in Ruby 2.7.0-preview1

There are couple of new features introduced to Ruby 2.7-preview, so we thought we should give it a try! You can do as well as we do.

Lets get started

As per the post on ruby lang news page, Official announcement. The release announced, talks about various new features and performance improvements. The Final release is planned for December, 2019.

Most notably of amoung them are:

REPL Improvements

REPL stands for Read-Evaluate-Print-Loop, the regular IRB console that you used to try out ruby for the first time. It has finally got some required features. Let me tell you it will be a huge success for all those who are trying to learn ruby or just trying it for the first time.

After these changes are available, you will able to scroll up through your classes/methods that you are trying to test on IRB, which you were unable to do on previous versions. Also, the classes/objects are now colorised.

Pattern Matching

Coming to pattern matching part, this one is introduced as experimental feature to ruby-2.7. From a ruby perspective, case/when is where you can match data. This is also allowed for other data types such as Array or Hash. we tried out a simpler snippets to test pattern matching.


a = 10

case a
  in 1
  in 10
(irb):1: warning: Pattern matching is experimental, and the behavior may change in future versions of Ruby!
=> :large


a = [1,2]

case a
  in [1,b]
   p b

(irb):1: warning: Pattern matching is experimental, and the behavior may change in future versions of Ruby!
=> 2
# Notice how 2 is assigned to b using pattern matching


a = { a: 10, b: { c: 20, d: 30 } }

case a
  in { a: 10, value }
   p value
(irb):1: warning: Pattern matching is experimental, and the behavior may change in future versions of Ruby!
{ c: 20, d: 30 }
=> { c: 20, d: 30 }
# Notice how { c: 20, d: 20} is assigned to `value` variable.

Type Comparison

a = "Hello"

case a
  in String => value # value will contain "hello"
   puts value
  in Integer => integer # if a is integer
   puts integer
  puts "Nothing matches"
(irb):2: warning: Pattern matching is experimental, and the behavior may change in future versions of Ruby!
 => nil

Note that If else block is not present and case doesn’t satisfy any of the condition this will lead to NoPatternMatchingError.

Numbered Parameter

According to this new change, a default block parameter will be made available in terms of number e.g @1. So, when iterating through list of elements on an array something like:

[1,2,3].each { puts @1 }
=> [1,2,3]

This might add confusion with existing instance variables we use in ruby, and it might take away the beauty of writing loops as

[1,2,3].each { |x| puts x }

Beginless Range

Using a typical range operator in ruby, i.e a..b we can define a range from a to b inclusive. If you want to save some time addressing a range from 0 all the way to a number say 3 this is where beginless range comes handy. For example:

 # define an array
 a = (1..10).to_a
 => [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

 # Address array from 1 to 3
 # In ruby 2.6 or earlier
 => [1, 2, 3]

 # In Ruby 2.7.0
 => [1, 2, 3]

 # Similarly, exclusive range can be addressed as
 => [1, 2]


['a', 'A'].tally
=> { 'a' => 1, 'A' => 1 } # easy ^_^

According to the feature discussion, there is another version proposed besides tally and that is tally_by which can take a method as a parameter and does the job accordingly. we found it very useful and handy to be honest. Although, tally_by is not yet accepted. Since, this method is defined in Enumerable module this is available to Hash as well.

As per the suggestion, tally_by was expected to do the following task:

['a', 'A'].tally_by(&:downcase)
=> { 'a' => 2 }

Let us wait for this make to the upcoming ruby versions by a different name.

Compaction GC

This release introduces Compaction GC which can defragment a fragmented memory space. What leads to fragmented memory?

Multi-threaded programs in ruby can cause these fragmentation in memory, which leads to high memory usage and degraded speed. So to overcome this GC.compact method is introduced in order to defrag the memory space.

An Illustration describing issue and solution:

Updates in ruby 2.7

Recommended Posts

Default Enum in Rails 6
Rails 6 provides a way to define default enum value. Let’s see how it works...
Ruby 2.7 adds Enumerable#tally
After introducing the Enumerable#tally method in Ruby 2.7-preview updates. #tally as the name suggests gives...
How to rename column name in Rails
Rails rename_column Rails provides a simple method rename_column which can be used in a migration....