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What's the science behind the fact that the to_i method in Ruby's NilClass instances returns zero? Returning nil or raising an exception would not be more logical?
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In Ruby, nil is a special value that denotes the absence of any value. Nil is an object of NilClass. nil is Ruby's way of referring to nothing or void.
Zero is a value, and ALL values in Ruby are evaluated to true, EXCEPT for FALSE and NIL.
nil? is a standard method in Ruby that can be called on all objects and returns true for the nil object and false for anything else. empty? is a standard Ruby method on some objects like Arrays, Hashes and Strings.
That's the easy part. In Ruby, you can check if an object is nil, just by calling the nil? on the object... even if the object is nil. That's quite logical if you think about it :) Side note : in Ruby, by convention, every method that ends with a question mark is designed to return a boolean (true or false).
It fits the Ruby philosophy of permissiveness (as opposed to, for example, the strictness of Python):
nil.to_i #=> 0
"".to_i #=> 0
"123hello".to_i #=> 123
"hello".to_i #=> 0
As noted by Zabba, you can use Kernel#Integer(string) for strict conversion.
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