Multiple rescue clauses in Ruby - Step-by-Step Execution

Concept Flow - Multiple rescue clauses

Start

↓

Try block

↓

Exception?

No→End

Yes↓

Rescue clause 1: matches?

No→Rescue clause 2: matches?

↓

Handle Exception

↓

End

The program tries code, checks for exceptions, and handles them with the first matching rescue clause, then ends.

Execution Sample

Ruby

begin
  1 / 0
rescue ZeroDivisionError
  puts "Zero division error caught"
rescue StandardError
  puts "Standard error caught"
end

This code tries to divide by zero, catches the ZeroDivisionError first, and prints a message.

Execution Table

Step	Action	Evaluation	Result
1	Execute begin block: 1 / 0	Raises ZeroDivisionError	Exception raised
2	Check rescue ZeroDivisionError	Matches exception	Rescue clause 1 runs
3	Execute rescue clause 1	puts message	Output: Zero division error caught
4	End of begin-rescue block	No more code	Program continues

💡 Exception handled by first matching rescue clause, program continues normally

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
exception	nil	ZeroDivisionError raised	Handled by rescue clause 1	Handled	nil

Key Moments - 2 Insights

Why does the first rescue clause run instead of the second?

Because the exception raised is ZeroDivisionError, which matches the first rescue clause exactly, so Ruby does not check further clauses (see execution_table step 2).

What happens if no rescue clause matches the exception?

The exception is unhandled and will cause the program to crash or propagate up (not shown in this example, but implied in concept_flow).

Visual Quiz - 3 Questions

Look at the execution table, what exception is raised at step 1?

A No exception

B StandardError

C ZeroDivisionError

D NameError

💡 Hint

Check the 'Evaluation' column in execution_table row 1

At which step does the program print the message 'Zero division error caught'?

A Step 3

B Step 1

C Step 2

D Step 4

💡 Hint

Look at the 'Result' column in execution_table row 3

If the exception was a RuntimeError, which rescue clause would run?

A Rescue clause 1 (ZeroDivisionError)

B Rescue clause 2 (StandardError)

C No rescue clause

D Both rescue clauses

💡 Hint

StandardError is a parent of RuntimeError, so rescue clause 2 matches (concept_flow and key_moments)

Concept Snapshot

begin
  # code that might raise
rescue ExceptionType1
  # handle ExceptionType1
rescue ExceptionType2
  # handle ExceptionType2
end

- Ruby tries rescue clauses in order.
- First matching rescue handles the exception.
- If none match, exception propagates.

Full Transcript

This example shows how Ruby handles multiple rescue clauses. The program tries to run code that divides by zero, which raises a ZeroDivisionError. Ruby checks the first rescue clause and finds it matches the exception, so it runs that rescue block and prints a message. It does not check further rescue clauses. If no rescue clause matched, the exception would be unhandled and cause an error. This step-by-step trace helps understand how Ruby picks the right rescue clause.