What is freeze in Ruby: Explanation and Examples

In Ruby, freeze is a method that makes an object immutable, meaning you cannot change it after freezing. Once an object is frozen, any attempt to modify it will raise a FrozenError.

How It Works

Think of freezing an object like putting it in a locked box. Once inside, you can't change anything about it. In Ruby, calling freeze on an object locks it so that no further changes can be made to it.

This is useful because it prevents accidental changes to important data. For example, if you have a string or array that should stay the same throughout your program, freezing it ensures it stays constant.

Under the hood, Ruby marks the object as frozen. If you try to modify it later, Ruby will stop you by raising an error, protecting the object's state.

Example

This example shows how freezing a string prevents it from being changed:

ruby

name = "Alice"
name.freeze

begin
  name << " Smith"
rescue => e
  puts e.message
end

Output

can't modify frozen String

When to Use

Use freeze when you want to protect data from being changed accidentally. This is common when you have constants or configuration data that should remain the same.

For example, freezing strings used as keys in hashes or freezing arrays of settings helps avoid bugs caused by unexpected modifications.

It also improves program safety by making your intentions clear: this object is meant to stay unchanged.

Key Points

• freeze makes an object immutable.
• Trying to change a frozen object raises a FrozenError.
• Useful for protecting constants and important data.
• Works on most Ruby objects like strings, arrays, and hashes.

Key Takeaways

The freeze method prevents any changes to an object after it is called.

Modifying a frozen object raises a FrozenError to protect data integrity.

Use freeze to safeguard constants and configuration data in your program.

Freezing clarifies your code's intent by marking objects as immutable.