From: Leslie Viljoen <leslieviljoen@...>
Date: 2010-04-06T23:44:50+09:00
Subject: Custom Exceptions

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Hi everyone

I want to make a custom exception like so:

class BillRowError < StandardError
    def initialize(field, index)
        @field = field
        @index = index
    end
end

I'll call this like so:
raise(BillRowError.new(:roamingcalls, @index), "Roaming Calls field
missing") if n.length == 0

But now I'd like to be able to modify the string that Ruby prints when the
exception is not rescue'd. I thought I could add this method to the
BillRowError class:

    def message
        @message + " field: #{@field}, row: #{@index}"
    end

That almost works but I get a "instance variable @message not initialized"
warning, which means Ruby is not setting @message in my object like I
expected. Making my own message= method doesn't help.

Can an exception object access and modify the message that gets passed in
the "raise"?

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