How Do Panics Behave in Deferred Functions in Go?

Panic Handling in Deferred Functions in Go

Panic handling in Go is a crucial aspect of error management. While it's commonly discouraged to panic from a destructor in C , it's safe and acceptable to panic from within a deferred function in Go.

Panic Propagation and Overwriting

In the provided code example:

<br>func sub(){</p>
<pre class="brush:php;toolbar:false">defer func (){
    panic(2)
}()
panic(1)

}

func main(){

defer func(){
    x:=recover()
    println(x.(int));
}()
sub()

}

The second panic(2) does not overwrite the first panic(1). Instead, both panics are propagated to the main function, where the deferred recovery function retrieves and prints the value from the first panic(1).

Panic Termination and Recovery

When a panic occurs within a deferred function, the panic sequence continues. However, if the deferred function recovers from the panic (with the recover() function), the panic sequence stops. This ensures that panics do not terminate the Go program prematurely.

Example: Multiple Deferred Panics and Recovery

As demonstrated in the following example:

<br>func main() {</p>
<pre class="brush:php;toolbar:false">defer func() {
    fmt.Println("Checkpoint 1")
    panic(1)
}()
defer func() {
    fmt.Println("Checkpoint 2")
    panic(2)
}()
panic(999)

}

Even though all deferred functions execute panic(), recovery is possible from any deferred function, as evident in the following modified example:

<br>defer func() {</p>
<pre class="brush:php;toolbar:false">recover()
fmt.Println("Checkpoint 1")
panic(1)

}()
defer func() {

recover()
fmt.Println("Checkpoint 2")
panic(2)

}()

In this case, the final panic sequence includes information about all panic values and indicates where recovery occurred.

Conclusion

Panic handling in deferred functions in Go provides flexibility and allows for the continuation of panicking sequences. The ability to recover from a deferred-panic ensures that panics do not prematurely terminate the program. Go programmers can leverage this mechanism to implement robust error handling strategies.

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