panic keyword allows a program to terminate immediately and provide feedback to the caller of the program. It should be used when a program reaches an unrecoverable state. This most commonly occurs when a bug of some kind has been detected and it’s not clear to the programmer how to handle the error.
pro main(): int = {
panic "Hello";
.echo("End of main"); //unreachable statement
}
In the above example, the program will terminate immediately when it encounters the panic keyword.
Output:
main.fol:3
routine 'main' panicked at 'Hello'
-------
Trying to acces an out of bound element of array:
pro main(): int = {
var a: arr[int, 3] = [10,20,30];
a[10]; //invokes a panic since index 10 cannot be reached
}
Output:
main.fol:4
routine 'main' panicked at 'index out of bounds: the len is 3 but the index is 10'
-------
a[10];
^-------- index out of bounds: the len is 3 but the index is 10
A program can invoke panic if business rules are violated, for example: if the value assigned to the variable is odd it throws an error:
pro main(): int = {
var no = 13;
//try with odd and even
if (no % 2 == 0) {
.echo("Thank you , number is even");
} else {
panic "NOT_AN_EVEN";
}
.echo("End of main");
}
Output:
main.fol:9
routine 'main' panicked at 'NOT_AN_EVEN'
-------