Quick Answer

Occurs when calling undefined methods on objects

Understanding the Issue

NoMethodError indicates you're trying to call a method that doesn't exist for that object type. Common causes include typos, wrong object types, or missing method definitions.

The Problem

This code demonstrates the issue:

Ruby Error 
# Problem: Undefined method
"hello".uppercase # NoMethodError

The Solution

Here's the corrected code:

Ruby Fixed 
# Solution 1: Check method name
"hello".upcase # Correct method

# Solution 2: Check object type
123.to_s.upcase # Works for integers

# Solution 3: Use respond_to?
obj.my_method if obj.respond_to?(:my_method)

Key Takeaways

Always verify method existence and object types.