[Solved] Review the following Invoker method snippet for executing commands with undo/redo support. Identify the bug that causes the redo stack to not clear correctly after a new command execution.... | OOP & Design Patterns

OOP & Design Patterns - Command Pattern - Undo/Redo, Request Queuing & Logging

Review the following Invoker method snippet for executing commands with undo/redo support. Identify the bug that causes the redo stack to not clear correctly after a new command execution.

def execute_command(self, command):
    command.execute()
    self.undo_stack.append(command)
    # Missing line here?

AExecuting the command twice accidentally

BNot appending the command to the undo stack

CFailing to clear the redo stack after executing a new command

DClearing the undo stack instead of the redo stack

Step-by-Step Solution

Solution:

Step 1: Understand redo stack behavior
Redo stack should be cleared when a new command is executed to prevent invalid redo states.
Step 2: Analyze the code snippet
The snippet executes the command and pushes it onto the undo stack but does not clear the redo stack.
Final Answer:
Failing to clear the redo stack after executing a new command -> Option C
Quick Check:
Redo stack must reset on new commands [OK]

Quick Trick: Redo stack clears on new commands to avoid stale redo [OK]

Common Mistakes:

MISTAKES

Thinking redo stack should never be cleared
Confusing undo and redo stack roles
Assuming command execution automatically clears redo stack

Trap Explanation:

PITFALL

Option B looks plausible but the undo stack is correctly appended; the bug is redo stack not cleared.

Interviewer Note:

CONTEXT

Tests ability to identify subtle bugs in undo/redo command invoker implementations.

Master "Command Pattern - Undo/Redo, Request Queuing & Logging" in OOP & Design Patterns

2 interactive learning modes - each teaches the same concept differently

Solution Trace

More OOP & Design Patterns Quizzes

Review the following Invoker method snippet for executing commands with undo/redo support. Identify the bug that causes the redo stack to not clear correctly after a new command execution.

Step 1: Understand redo stack behavior

Step 2: Analyze the code snippet

Final Answer:

Quick Check:

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