Frozen objects in Ruby

Introduction

Freezing an object in Ruby means making it unchangeable. This helps keep data safe from accidental changes.

When you want to make sure a configuration value never changes during the program.

When sharing data between parts of a program and want to avoid accidental edits.

When you want to improve performance by preventing unnecessary copies of objects.

When debugging to catch unexpected changes to important objects.

Syntax

Ruby

object.freeze

Calling freeze on an object makes it immutable.

If you try to change a frozen object, Ruby raises a FrozenError.

Examples

Freezing a string prevents adding more text to it.

Ruby

str = "hello"
str.freeze
str << " world"  # This will cause an error

Freezing an array stops changing its elements.

Ruby

arr = [1, 2, 3]
arr.freeze
arr[0] = 10  # This will cause an error

Freezing a number does nothing because numbers can't be changed anyway.

Ruby

num = 100
num.freeze
# Numbers are already immutable, so freezing has no effect

Sample Program

This program freezes a string and then tries to change it. Ruby raises an error, which we catch and print. Finally, it prints the original string.

Ruby

name = "Alice"
name.freeze

begin
  name << " Smith"
rescue => e
  puts "Error: #{e.message}"
end

puts name

Important Notes

Freezing only affects the object itself, not objects inside it. For example, freezing an array does not freeze the objects inside the array.

You can check if an object is frozen by calling object.frozen?.

Summary

Freezing makes objects unchangeable to protect data.

Trying to change a frozen object causes an error.

Use freeze to keep important data safe from accidental changes.