Ruby Frozen String Literals: Past, Present, Future?

6 months ago

Ruby strings are mutable by default, unlike in many other programming languages where strings are immutable.
Frozen string literals (`# frozen_string_literal: true`) optimize performance by preventing unnecessary string duplications.
Ruby supports both mutable and immutable strings, leveraging frozen strings for optimizations like string views and hash key storage.
The `# frozen_string_literal: true` magic comment was introduced in Ruby 2.3 to prepare for Ruby 3.0's planned default frozen strings.
Performance benefits of frozen string literals include reduced memory allocations and improved execution speed, as seen in benchmarks like Lobsters (8-9% faster).
Chilled string literals were introduced in Ruby 3.4 to emit deprecation warnings for mutable string literals, paving the way for future default freezing.
Community adoption of frozen string literals is widespread, but some Ruby core members oppose making them the default due to compatibility concerns.
Alternatives to default frozen strings include directory-based compiler options, but these may fragment Ruby's behavior.
Matz has not committed to a timeline for making frozen string literals the default, leaving the future of this feature uncertain.

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