Suggestions how to use contracts

[Aarti_pl]

Hello!

I have a difficulty with defining strict boundary between 
preconditions/postconditions and regular errors throwing by function.

Can you share your strategies? How to divide checks in proper way, 
remembering that preconditions and postconditions are stripped from code 
in release mode.

Example:
class Evaluator {
public:
	int evaluate(char[] expression)
	in {
		assert(expression !="");
		assert(m_active);
	}

	body {
	}
private:
	bool m_active;
}

Function evaluate can be called only when m_active is true. Should this 
condition be checked from preconditions block or from body block with
if (!m_active) throw new Exception("Evaluator is not active.");

"m_active" depends on some other logic, either set by user or by other 
classes.


BR
Marcin Kuszczak
(Aarti_pl)