Course of Raku / Objects, I/O, and exceptions / Exceptions / Custom exceptions / Exercises / Too big

Solution: Too big

Here is a possible solution to the task.

Code

class TooBig is Exception {
    has $.value;
    has $.limit;

    method message {
        "Value $.value exceeds the limit of $.limit";
    }
}

my $limit = 50;

for 30, 99, 60 -> $value {
    TooBig.new(value => $value, limit => $limit).throw if $value > $limit;
    say "Value $value is within the limit";

    CATCH {
        when TooBig {
            say .message;
            say "Try a value up to {.limit}.";
        }
    }
}

🦋 You can find the source code in the file too-big.raku.

Output

Value 30 is within the limit
Value 99 exceeds the limit of 50
Try a value up to 50.
Value 60 exceeds the limit of 50
Try a value up to 50.

Comments

1. TooBig is Exception makes the class a throwable exception. It carries two pieces of data, value and limit, and its message method weaves both into the reported text.

2. .throw raises the exception, and when TooBig matches it by type. The handler does more than print the message: it reads the limit attribute straight off the caught object to give a helpful hint. That is the advantage of a custom exception over a plain string — the handler receives structured data it can act on.

3. The exception is thrown only when $value > $limit. For 30, no exception is raised and the loop body runs to its say, printing that the value is within the limit. For 99 and 60, the throw fires, so that say is skipped and the CATCH handles it instead. The for body is itself the block the CATCH guards, so a caught exception ends only the current iteration — the loop then simply moves on to the next value.

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