Untrapped Error

MartinRinehart

I'm writing a console. You input 2+2 and it outputs 2+2 # 4. Problem is, your input may not be perfect, so a little error trapping is needed.

In this part of the process() function (line #s added):


59    results = []
60    for line in lines do
61        rslt = line.chomp() + ' # '
62        begin
63            rslt += eval(line).to_s().chomp()
64        rescue => e
65            rslt += e.to_s().chomp()
66        end
67    
68        results.push( qq(rslt) ) 
69    end # loop over lines

I'm thinking that an error at line 63 gets caught and reported at line 65. It usually does. Now, however, I've got this:

Any ideas why this isn't caught by the rescue statement? Any ideas on how to catch it?

todd burch

From the Pickaxe Book: (Ruby 1.8, page 110)

@unknownuser said:

"If you write a rescue clause with no clause parameter list, the parameter defaults to StandardError"

You got a SyntaxError, which is part of ScriptError, not StandardError.

Try this:

rescue Exception => e

to catch everything.

MartinRinehart

@unknownuser said:

rescue Exception => e

to catch everything.

I don't want to seem ungrateful, but that upgraded me to Bug Splat. Is there a

rescue BugSplat => e

???

todd burch

Do you have access to the pickaxe book? Try ScriptError. Try a stepladder of all the exception subclasses with multiple rescues.

Dan Rathbun

@martinrinehart said:


> 64  rescue => e
> 65    rslt += e.to_s().chomp()
> 66  end
>

Your local reference e receives a pointer to an Exception object from the rescue clause, not a String object.

You should use the instance method Exception.message to get the exception's string, like this:
65 rslt << e.message.chomp()

(As a side-note on Optimization, generally speaking, + and += String concatenation, require Ruby to create at least one extra String object than String append <<. Ruby internally converts a+=b to a=a+b, OR a+='literal' to a=a+'literal', so using += doesn't gain you anything over <<, and may be twice as slow or more, in a loop.)