Rambling: try/catch

Ruby
1

Just had an vague idea about generic java “try-catch” converted to ruby-
world I would like some feedback on.

I’m building a “microscopic CMS” system to learn more ruby, and of
course
it would be good to implement proper error catching system. Try-catch is
what java uses.

Now the vague idea was to create one error catching function, and to
throw all things that might fail (say loading a file) “through” that
function. Passed as a code block? I am not sure, it keeps slipping from
me. :slight_smile:

What do you think?

2

On Nov 7, 12:40 pm, Casimir P [email protected] wrote:

me. :slight_smile:

What do you think?

–
Casimir P.
Art Portfolio:http://csmr.dreamhosters.com

I’m not sure I completely understand (I’ve had a string of wrong
answers here recently), but I think you’re looking for begin/rescue:

begin
do_something_that_might_explode()
rescue => e
puts “uh-oh, an exception: #{e}: #{e.backtrace.join(”\n")}"
end

3

On Nov 7, 2007, at 1:45 PM, Casimir P wrote:

Now the vague idea was to create one error catching function, and to
throw all things that might fail (say loading a file) “through” that
function. Passed as a code block? I am not sure, it keeps slipping
from
me. :slight_smile:

I think this is what you’re looking for:

begin

do something useful…

rescue => e

do something with the error ‘e’

end

To keep rescue code short, you could have a function:
error_function = lambda { | error |
#do something useful…
}

and then for rescue…

begin
…
rescue => e
error_function[e]
end

Tadah!

HTH,
ari

4

Casimir P [email protected] writes:

me. :slight_smile:

What do you think?

–
Casimir P.
Art Portfolio: http://csmr.dreamhosters.com

The idea of passing around a signal handler is not new.
It allows you to handle low-level condition in a high-level manner.

Here is one, done à la SRFI-34.

def with_exception_handler(k = nil)
begin
yield
rescue Exception => e
if k then if k.call(e) == :retry then retry end end
end
end

limited_patience_handler =
lambda {
# can be called to handle exception three times.
# after that it loses patience and just reraise things.
i=[1,2,“last one”]
lambda{|e| if not i.empty?
puts “Got exception ##{i.shift}: #{e.inspect}”
:retry
else
puts “I’m done covering for you. Reraising to my
supervisor”
raise e
end}}.call

with_exception_handler(limited_patience_handler) {
puts “Raising”
raise “Test exception”
puts “Never reach here”
}

****Output:

Raising
Got exception #1: #<RuntimeError: Test exception>
Raising
Got exception #2: #<RuntimeError: Test exception>
Raising
Got exception #last one: #<RuntimeError: Test exception>
Raising
I’m done covering for you. Reraising to my supervisor
/tmp/x.rb:24: Test exception (RuntimeError)
from /tmp/x.rb:3:in `with_exception_handler’
from /tmp/x.rb:22

YS