Mastering Go's Panic and Recover Mechanism

Go's panic and recover functions are powerful tools for handling unexpected and unrecoverable errors. Understanding how they work is crucial for building robust Go applications that can gracefully handle runtime failures. This challenge will guide you through implementing and observing the behavior of panic and recover.

Problem Description

Your task is to implement a scenario in Go that demonstrates the use of panic and recover. You will need to:

1. Create a function that intentionally panics: This function should signal a critical, unrecoverable error.
2. Implement a deferred function that recovers: This deferred function should be designed to catch the panic and gracefully handle the situation.
3. Observe the execution flow: Understand how control is transferred when a panic occurs and how recover brings it back.

Key Requirements:

• The main program should start, call a function that panics, and then demonstrate that execution continues after the panic is recovered.
• The deferred function must use recover() to capture the panic value.
• The recovered value should be printed to demonstrate that the panic was caught.
• The program should print messages indicating the start and end of execution, as well as messages before and after the panic occurs.

Expected Behavior:

The program should print messages in a specific order, showing that the deferred function executes and recovers from the panic, allowing the main function to continue.

Edge Cases to Consider:

• What happens if recover is called in a function that did not panic?
• What happens if panic is called with different types of values (e.g., nil, string, error)?

Examples

Example 1: Basic Panic and Recover

package main

import "fmt"

func causePanic() {
	fmt.Println("Inside causePanic: About to panic!")
	panic("something went terribly wrong")
	fmt.Println("Inside causePanic: This will not be printed.")
}

func main() {
	fmt.Println("main: Starting execution.")
	defer func() {
		fmt.Println("main: Deferred function executing.")
		if r := recover(); r != nil {
			fmt.Printf("main: Recovered from panic: %v\n", r)
		}
		fmt.Println("main: Deferred function finished.")
	}()
	causePanic()
	fmt.Println("main: Execution continues after causePanic.")
	fmt.Println("main: Finishing execution.")
}

Expected Output 1:

main: Starting execution.
Inside causePanic: About to panic!
main: Deferred function executing.
main: Recovered from panic: something went terribly wrong
main: Deferred function finished.
main: Execution continues after causePanic.
main: Finishing execution.

Explanation 1:

The main function starts, prints its initial message, and then defers a function. When causePanic is called, it prints its message and then panics with a string. The panic immediately stops the execution of causePanic and unwinds the call stack. The deferred function in main is then executed. Inside this deferred function, recover() is called, which catches the panic value ("something went terribly wrong"). This value is printed, and the deferred function completes. Because the panic was recovered, execution resumes in main after the call to causePanic, and the remaining lines of main are executed.

Example 2: Panic with a different type

package main

import "fmt"

func causeErrorPanic() {
	fmt.Println("Inside causeErrorPanic: About to panic with an error!")
	panic(fmt.Errorf("custom error: data not found"))
	fmt.Println("Inside causeErrorPanic: This will not be printed.")
}

func main() {
	fmt.Println("main: Starting execution.")
	defer func() {
		fmt.Println("main: Deferred function executing.")
		if r := recover(); r != nil {
			fmt.Printf("main: Recovered from panic: %T %v\n", r, r)
		}
		fmt.Println("main: Deferred function finished.")
	}()
	causeErrorPanic()
	fmt.Println("main: Execution continues after causeErrorPanic.")
	fmt.Println("main: Finishing execution.")
}

Expected Output 2:

main: Starting execution.
Inside causeErrorPanic: About to panic with an error!
main: Deferred function executing.
main: Recovered from panic: *errors.errorString custom error: data not found
main: Deferred function finished.
main: Execution continues after causeErrorPanic.
main: Finishing execution.

Explanation 2:

Similar to Example 1, this demonstrates that panic can accept values of type error. The recover() function correctly captures the error object, and we print its type and value.

Constraints

• The solution must be written in the Go programming language.
• The code should compile and run without errors using a standard Go toolchain.
• The output must strictly follow the order and content shown in the examples.
• You should not use any external libraries beyond the standard Go library (e.g., fmt).

Notes

• panic is intended for truly exceptional situations that cannot be handled by normal error propagation.
• recover only works when called directly inside a deferred function.
• A panic that is not recovered will cause the program to terminate.
• Consider how you might handle different types of values passed to panic.