Why strings are mutable in Ruby - Challenge Your Understanding

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Ruby code?

Consider the following Ruby code that modifies a string. What will be printed?

Ruby

str = "hello"
str.upcase!
puts str

A Error: undefined method

B hello

C HELLO\n

D HELLO

💡 Hint

The method upcase! changes the string itself if possible.

In Ruby, strings are mutable, so methods ending with ! modify the original string. upcase! changes all letters to uppercase in place.

🧠 Conceptual

intermediate

Why are Ruby strings mutable?

Why does Ruby allow strings to be changed after creation?

A Because Ruby strings are stored as immutable objects internally

B To improve performance by avoiding creating new objects for every change

C To prevent accidental changes to string data

D Because strings are always constants in Ruby

💡 Hint

Think about how changing strings without creating new ones affects speed and memory.

Ruby strings are mutable to allow efficient modifications without creating new string objects each time, improving performance.

🔧 Debug

advanced

What error does this Ruby code raise?

What error will this code produce and why? code: str = "hello" str.freeze str << " world"

A SyntaxError: unexpected <<

B No error, output: "hello world"

C RuntimeError: can't modify frozen String

D TypeError: can't convert String into Integer

💡 Hint

Freezing an object prevents changes to it.

Calling freeze on a string makes it immutable. Trying to append with << raises a RuntimeError.

❓ Predict Output

advanced

What is the output of this Ruby code with string mutation?

What will this Ruby code print?

Ruby

a = "cat"
b = a
b.upcase!
puts a

A CAT

B cat

C CAT\ncat

D Error: undefined method

💡 Hint

Variables a and b point to the same string object.

Both a and b refer to the same string. upcase! changes the string in place, so a also shows the change.

🧠 Conceptual

expert

How does Ruby's string mutability affect memory usage?

Which statement best explains how Ruby's mutable strings impact memory?

A Mutable strings reduce memory use by modifying existing objects instead of creating new ones

B Mutable strings increase memory use because each change creates a new copy

C Mutable strings have no effect on memory because Ruby uses garbage collection

D Mutable strings cause memory leaks by never freeing old string data

💡 Hint

Think about how changing strings in place affects object creation.

Because Ruby strings can be changed in place, fewer new objects are created, saving memory.