Question

New to Ruby, and I’m trying to figure out what idiom to use to restrict some integer values to the constructor of a class.

From what I’ve done so far, if I raise an exception in initialize(), the object is still created but will be in an invalid state (for example, some nil values in instance variables). I can’t quite see how I’m supposed to restrict the values without going into what looks unnecessarily big steps like restricting access to new().

So my question is, by what mechanism can I restrict the range of values an object is instantiated with?

Answer 1

Huh, you are entirely correct that the object still lives even if initialize raises an exception. However, it will be quite hard for anyone to hang on to a reference unless you leak self out of initialize like the following code I just wrote does:

>> class X
>>   def initialize
>>     $me = self
>>     raise
>>   end
>>   def stillHere!
>>     puts "It lives!"
>>   end
>> end
=> nil
>> t = X.new
RuntimeError: 
    from (irb):14:in `initialize'
    from (irb):20:in `new'
    from (irb):20
>> t
=> nil
>> $me
=> #<X:0xb7ab0e70>
>> $me.stillHere!
It lives!