Exception hierarchy in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the root class for all exceptions in Ruby?

The root class for all exceptions in Ruby is <code>Exception</code>. All other exception classes inherit from it.

intermediate

What is the difference between StandardError and Exception in Ruby?

<code>StandardError</code> is a subclass of <code>Exception</code> and is the default for rescue clauses. Most common errors inherit from <code>StandardError</code>, while <code>Exception</code> includes system errors that are usually not rescued.

beginner

Name two common subclasses of StandardError.

Two common subclasses of StandardError are NoMethodError (raised when calling a method that doesn't exist) and ArgumentError (raised when wrong arguments are passed to a method).

intermediate

Why should you avoid rescuing Exception directly in Ruby?

Rescuing Exception catches all exceptions, including system errors like Interrupt or SystemExit, which can prevent your program from exiting properly. It's safer to rescue StandardError or specific exceptions.

intermediate

What class do syntax errors belong to in Ruby's exception hierarchy?

Syntax errors belong to the <code>SyntaxError</code> class, which inherits directly from <code>ScriptError</code>, a subclass of <code>Exception</code>. They are not subclasses of <code>StandardError</code>.

Which class is the parent of most common Ruby exceptions?

A Exception

B StandardError

C RuntimeError

D ScriptError

Most common exceptions inherit from StandardError, which itself inherits from Exception.

What happens if you rescue Exception in Ruby?

A You rescue only syntax errors

B You rescue only runtime errors

C You rescue all exceptions, including system errors

D You rescue only standard errors

Rescuing Exception catches all exceptions, including system-level ones like Interrupt.

Which class is NOT a subclass of StandardError?

A NoMethodError

B ArgumentError

C RuntimeError

D SyntaxError

SyntaxError inherits from ScriptError, not StandardError.

Which exception class is used for errors raised when a method is called with wrong arguments?

A ArgumentError

B NameError

C TypeError

D NoMethodError

ArgumentError is raised when wrong arguments are passed to a method.

Which class is the direct parent of SyntaxError?

A ScriptError

B StandardError

C Exception

D RuntimeError

SyntaxError inherits directly from ScriptError.

Explain the Ruby exception hierarchy starting from Exception down to common error classes.

Think about which exceptions are rescued by default and which are not.

Why is it recommended to rescue StandardError instead of Exception in Ruby?

Consider what happens if you catch all exceptions including system interrupts.