Where are catch and throw useful in Ruby?

Question

I really don\'t see a sane use for these. There is already rescue and raise, so why the need for throw and catch? It seem

Answer 1

They can be really useful in simplifying DSLs for end users by passing control out of the DSL without the need for complex case / if statements

I have a Ruby app which allows users to extend it via an internal DSL. Some of the functions in the DSL need to return control to specific parts of my application. Let's take a simple example. Suppose the user is developing a simple extension concerning dates

if today is a holiday then
   do nothing
end

week_of_year = today.week.number

if week_of_year < 10 then

...

The do nothing bit triggers a throw which passes control out of the exec statement and back to me.

Rather than continuing to execute the DSL, on some condition, we want it to exit and hand control back to my application. Now you could get the user to use lots of embedded if statements and have the DSL end naturally but that just obscures what the logic is trying to say.

Throw really is a goto which is 'considered dangerous' but damn it sometimes they are the best solution.