Nithin Bekal

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What's new in Ruby 2.4?

25 Dec 2016

It’s Christmas day, and following the tradition of the last few years, the Ruby core team have released a new Ruby version today. I’ll summarize some of the interesting new features in Ruby 2.4 here.

Previous: Ruby 2.3.


Fixnum and Bignum have been unified into Integer class.

So far, we’ve had two classes for storing integers - Fixnum for small integers, and Bignum for numbers outside this range. However, these are implementation details that programmers don’t need to worry about while writing code.

These two classes have been replaced by a single Integer class. Previously, Integer was a superclass of these two classes, but now both Fixnum and Bignum are aliases to Integer.

# 2.3
42.class      #=> Fixnum
(2**62).class #=> Bignum

# 2.4
42.class      #=> Integer
(2**62).class #=> Integer

Fixnum == Integer #=> true
Bignum == Integer #=> true

New Integer#digits method

42.digits  #=> [2, 4]

Precision for float modifiers

Float methods like #ceil, #floor, #truncate and #round take an optional argument to set precision.

1.567.round       #=> 2
1.567.round(2)    #=> 1.57
123.456.round(-1) #=> 120

Float#round default behavior remains unchanged

This one isn’t really a change, but this change in default behavior initially made it to one of the preview releases, and was reverted later on.

By default, #round uses round-half-up behavior, ie. 1.5 would be rounded to 2. The new behavior was to use banker’s rounding, which rounds half to nearest even number. This might cause bugs in many existing applications which rely on half-up rounding, so the original default has been retained.

# suggested behavior
1.5.round  #=> 2
2.5.round  #=> 2

# actual behavior
1.5.round #=> 2
2.5.round #=> 3

Float#round options

Even though the round-to-nearest-even change was reverted, new options were introduced in Float#round that allow you to explicitly set what kind of rounding to use.

2.5.round               #=> 3
2.5.round(half: :even)  #=> 2
2.5.round(half: :down)  #=> 2
2.5.round(half: :up)    #=> 3


I’m a big fan of the pry gem for the binding.pry method that opens a REPL while running your code. IRB has now introduced this feature, and ruby now opens a REPL when it encounters the binding.irb method.



This method, and the bang version, #compact!, remove keys with nil values from the hash.

{ a: "foo", b: false, c: nil }.compact
#=> { a: "foo", b: false }


Applies the block for each value in the hash. Also provides a #transform_values! method that modifies the existing hash. Examples from the docs:

h = { a: 1, b: 2, c: 3 }
h.transform_values {|v| v * v + 1 }  #=> { a: 2, b: 5, c: 10 }
h.transform_values(&:to_s)           #=> { a: "1", b: "2", c: "3" }

Strings, Symbols and IO

String supports unicode case mappings

Until now, Ruby only performed case conversion on ASCII characters. The upcase, downcase, swapcase, capitalize methods on String and Symbol have now been extended to work with unicode characters.

# 2.3
"Türkiye".upcase   #=> "TüRKIYE"
"TÜRKİYE".downcase #=> "tÜrkİye"

# 2.4
"Türkiye".upcase   #=> "TÜRKIYE"
"TÜRKİYE".downcase #=> "türki̇ye"

Specify string buffer size now allows a capacity argument to specify the size of the buffer. This will have performance benefits when the string will be concatenated many times.'foo', capacity: 1_000)

Symbol#match now works like String#match

Symbol#match used to return the match position, while String#match returned a MatchData object. This has been fixed in 2.4 and now both return a MatchData.

# 2.3
:hello_ruby.match(/ruby/) #=> 6

# 2.4
:hello_ruby.match(/ruby/) #=> #<MatchData "ruby">

IO#gets and other methods get a chomp flag

You can now add an optional chomp: true flag to #gets, #readline, #each_line, #readlines and IO.foreach.

# In 2.3, you did this
foo = gets.chomp

# 2.4
foo = gets(chomp: true)



This new method returns true or false without updating the $~ global variable. Since it doesn’t create a MatchData object or update $~, it performs better than #match.

/foo/.match?('foo')  #=> true
$~                   #=> nil


Returns a hash representing information about the named captures.

/(?<fname>.+) (?<lname>.+)/.match('Ned Stark').named_captures
#=> {"fname"=>"Ned", "lname"=>"Stark"}



(1..5).sum         #=> 15
%w(a b c).sum('')  #=> "abc"

Files and directories

The #empty? method was added to Dir, File and Pathname.

Dir.empty?('path/to/some/dir')     #=> true
File.empty?('path/to/some/file')   #=> true'file-or-dir').empty? #=> true

Language features

Multiple assignment in conditionals

In Ruby 2.3, you would get a syntax error if you tried multiple assignment in a conditional. This has been changed to a warning instead.

# 2.3
if (a,b = [1,2]) then 'yes' else 'no' end
#=> SyntaxError: (irb):9: multiple assignment in conditional

# 2.4

if (a,b = [1,2]) then 'yes' else 'no' end
#=> warning: found = in conditional, should be ==
#=> 'yes'

if (a,b = nil) then 'yes' else 'no' end
#=> warning: found = in conditional, should be ==
#=> 'no'

Wrapping up

I haven’t mentioned all the new features in Ruby 2.4 here, but if you’re interested in the complete list of changes, take a look at the Ruby 2.4.0 NEWS file.

Here are some more articles covering the new release:

Hi, I’m Nithin Bekal, a software craftsman with over 7 years of experience in shipping web applications. I mostly use Ruby, but lately have also been exploring Elixir. Co-founder of, and helping organize Rubyconf India. Tweet to me at @nithinbekal.