NameError

NameError is raised when Ruby encounters a name (variable, constant, or method) that it doesn't recognize. This is different from NoMethodError which specifically involves methods on objects.

Common causes

• Using a variable before it is defined
• Typo in variable or constant name
• Referencing a constant from wrong namespace
• Missing require for a class/module
• Variable defined in different scope

How to fix it

• Check for typos in variable/constant names
• Ensure variables are defined before use
• Use fully qualified constant names: Module::Class
• Add require statements for external dependencies
• Check variable scope (local, instance, class)

Example

# Error example
puts user_name  # => NameError: undefined local variable or method 'user_name'

# Fix by defining the variable first
user_name = "Alice"
puts user_name  # => "Alice"

# Constant example
MyApp::User  # => NameError if MyApp module not defined

Related errors