The Evolution of Ruby Strings from 1.8 to 2.5


In Ruby, a string is represented as an instance of the String class. This class has highly evolved between Ruby 1.8 and Ruby 2.5.

So, the purpose of this article is to detail the main changes that occurred for each major release.

Feel free to let a comment if you want to share additional informations.

1.8 to 1.9

Let’s have a look to what are the main differences for the String class between 1.8 and 1.9

The first difference is that the Enumerable module is included in the String class in Ruby 1.8 when it’s not included anymore in Ruby 1.9.

The second difference is that a bunch of new instance methods are available for the String class in Ruby 1.9.

Feel free to read the Ruby Object Model article if you are unfamiliar with the Object class and the ancestor chain.

But the most important change remains in the fact that in Ruby 1.8 strings are considered as a sequence of bytes when in Ruby 1.9 strings are considered as a sequence of codepoints.

A sequence of codepoints, coupled to a specific encoding, allows Ruby to handle encodings.

In effect, on disk, a string is stored as a sequence of bytes.

An encoding simply specifies how to take those bytes and convert them into codepoints.

So, from Ruby 1.9, Ruby natively handle string encoding when in 1.8 the iconv library was required to do this job.

Note that the default encoding of each string is Binary (read as a sequence of bytes).

Note that the iconv library is deprecated in Ruby 1.9

1.9 to 2.0

In Ruby 2.0, UTF8 is the default encoding of each string of a running program.

In effect, in Ruby 2.0 the default encoding is UTF8 when in 1.9 it was Binary.

This behavior is a bit similar with Java which uses UTF16 as default encoding.

Note that from Ruby 2.0, the iconv library is no longer part of the language.

2.0 to 2.1

In Ruby 2.0, encoding a string from an encoding to the same one — UTF8 to UTF8 for example — results in a no-op

Here we can see that in Ruby 2.0, a UTF8 string that we explicitly encode in UTF8 returns the string without replacing the unknown codepoints. So the invalid: :replace operation is omitted.

In Ruby 2.1, the invalid: :replace operation is processed and the default characters Replaces each invalid codepoint in the sequence.

2.1 to 2.5

Since Ruby 2.1 and in addition to providing many performance improvements, the String class added two main features:

The frozen_string_literal: true magic comment (since Ruby 2.3)

Case conversion for non ASCII strings (since Ruby 2.4)

Benchmark string allocations

The following benchmark is made by using the benchmark-ips gem

and it produces the following result for each version of Ruby — from the 1.8 to the 2.5

Here we can see that string allocation in ruby 2.5 is about 4 times more efficient than in Ruby 1.8


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