Boost C++ Libraries

Description

This is used to specify postconditions, exception guarantees, old value copies at body, and check class invariants for destructors (destructors cannot have preconditions, see Destructor Calls):

class u {
    friend class boost::contract::access;

    void invariant() const { // Optional (as for static and volatile).
        BOOST_CONTRACT_ASSERT(...);
        ...
    }

public:
    ~u() {
        boost::contract::old_ptr<old_type> old_var;
        boost::contract::check c = boost::contract::destructor(this)
            // No `.precondition` (destructors have no preconditions).
            .old([&] { // Optional.
                old_var = BOOST_CONTRACT_OLDOF(old_expr);
                ...
            })
            .postcondition([&] { // Optional.
                BOOST_CONTRACT_ASSERT(...);
                ...
            })
            .except([&] { // Optional.
                BOOST_CONTRACT_ASSERT(...);
                ...
            })
        ;

        ... // Destructor body.
    }
    
    ...
};

For optimization, this can be omitted for destructors that do not have postconditions and exception guarantees, within classes that have no invariants.

See Also:

Destructors