Ensure for cleanup in Ruby - Step-by-Step Execution

Concept Flow - Ensure for cleanup

Start

↓

Try block runs

↓

Exception?

Yes→Handle exception or skip

↓

Exception handled

↓

Ensure block runs ALWAYS

↓

End

The ensure block runs no matter what happens in the try block, even if an error occurs, to clean up resources.

Execution Sample

Ruby

begin
  puts "Start"
  raise "Error"
ensure
  puts "Cleanup"
end

This code prints 'Start', then raises an error, but still runs the ensure block to print 'Cleanup'.

Execution Table

Step	Action	Output	Exception Raised?	Ensure Block Run?
1	Enter begin block	None	No	No
2	Execute puts "Start"	Start	No	No
3	Raise exception	None	Yes	No
4	Run ensure block	Cleanup	Yes	Yes
5	Exception propagates after ensure	None	Yes	No

💡 Exception raised at step 3, ensure block runs at step 4, then exception propagates.

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
exception_raised	false	false	true	true	true
ensure_ran	false	false	false	true	true

Key Moments - 2 Insights

Why does the ensure block run even after an exception is raised?

Because the ensure block is designed to always run after the begin block, regardless of exceptions, as shown in execution_table step 4.

Does the ensure block stop the exception from propagating?

No, the ensure block runs but does not catch or stop the exception; the exception continues after ensure, as seen in step 5.

Visual Quiz - 3 Questions

Look at the execution_table, at which step does the ensure block run?

A Step 4

B Step 3

C Step 2

D Step 5

💡 Hint

Check the 'Ensure Block Run?' column in execution_table.

According to variable_tracker, when does 'exception_raised' become true?

A After Step 2

B After Step 3

C After Step 4

D At Start

💡 Hint

Look at the 'exception_raised' row and its values after each step.

If the raise line is removed, what changes in the execution_table?

A Output 'Cleanup' will not appear

B Ensure block will not run

C Exception Raised? column will be 'No' for all steps

D Program will stop at step 3

💡 Hint

Without raise, no exception occurs, so check 'Exception Raised?' column.

Concept Snapshot

Ruby's ensure block runs after begin block code, no matter what.
It runs even if an exception is raised.
Use ensure to clean up resources like files or connections.
Ensure does not catch exceptions; it just guarantees cleanup.
Syntax:
begin
  # code
ensure
  # cleanup code
end

Full Transcript

This visual trace shows how Ruby's ensure block works. The program starts and runs the begin block. It prints 'Start' then raises an error. Even though an exception occurs, the ensure block runs next and prints 'Cleanup'. After that, the exception continues to propagate. Variables track that the exception was raised at step 3 and the ensure block ran at step 4. Key points: ensure always runs, even after errors, but does not stop exceptions. The quiz asks about when ensure runs, when exception_raised becomes true, and what changes if the raise is removed.