Ruby: Custom Errors for Lazy Bums with const_missing

Catching errors is quite a normal thing when writing code, every programing language has some variation of the throw/catch, in Ruby's case, it's the elegant begin, rescue and ensure blocks.

At some point in every project you stop catching "other" people's errors and start catching your own.

So you start creating you own error classes, there's a couple common approaches I've seen over the years.

• Create an Errors namespace on each class/module you need and create errors for that there.
• Create a generic Project::Errors with its own file bag and throw all errors in there.

I usually go for the second approach, so error classes don't distract me, but that's more of a personal preference anyway.

However, I am a lazy bum and I've got tired of specified my error classes, so I made this Gist as an example:

	#The following two examples are equivalent
	#Example 1, explicit error classe declaration
	class MyMainNamespace
	module Errors
	class Error1 < StandardError; end
	class Error2 < StandardError; end
	end
	end
	#Example 2, use const_missing for maximum lazyness
	class MyMainNamespace
	module Errors
	def self.const_missing class_name
	self.const_set( class_name , Class.new( StandardError ) )
	self.const_get( class_name )
	end
	end
	end
	#usage:
	being
	do_something
	rescue MyMainNamespace::Errors::Error1
	do_something_else
	rescue MyMainNamespace::Errors::Error2
	do_something_different
	#only works with second example, throws an invalid constant Error404 otherwise
	rescue MyMainNamespace::Errors::Error404
	error_not_found
	end

view raw errorclasses hosted with ❤ by GitHub

The main idea behind this, is letting you freely type your errors as you need them both where they're being raised and rescued and you don't need to worry about they existing since they'll be created in runtime for you.

This method is probably not very efficient, but I don't care for this case.