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## Class template specify_postcondition_except

boost::contract::specify_postcondition_except — Allow to specify postconditions or exception guarantees.

## Synopsis

    // In header: <boost/contract/core/specify.hpp>

    template<typename VirtualResult = void>
    class specify_postcondition_except {
    public:
      // construct/copy/destruct
      ~specify_postcondition_except();

      // public member functions
      template<typename F> specify_except postcondition(F const &);
      template<typename F> specify_nothing except(F const &);
    };

## Description

Allow to specify functors this library will call to check postconditions or exception guarantees. This object is internally constructed by the library when users specify contracts calling `boost::contract::function` and similar functions (that is why this class does not have a public constructor).

See Also:

Postconditions, Exception Guarantees

### Template Parameters

1.     typename VirtualResult = void

   Return type of the enclosing function declaring the contract if that is either a virtual or an overriding public function, otherwise this is always `void`. (Usually this template parameter is automatically deduced by C++ and it does not need to be explicitly specified by programmers.)

### `specify_postcondition_except` public construct/copy/destruct

1.     ~specify_postcondition_except();

   Destruct this object.

   Throws: This is declared `noexcept(false)` since C++11 to allow users to program failure handlers that throw exceptions on contract assertion failures (not the default, see Throw on Failure).

### `specify_postcondition_except` public member functions

1.     template<typename F> specify_except postcondition(F const & f);

   Allow to specify postconditions.

   Parameters:

   `f`

   Functor called by this library to check postconditions `f()` or `f(result)`. Assertions within this functor are usually programmed using ``BOOST_CONTRACT_ASSERT``, but any exception thrown by a call to this functor indicates a contract assertion failure (and will result in this library calling ``boost::contract::postcondition_failure``). This functor should capture variables by (constant) references (to access the values they will have at function exit). This functor must be a nullary functor `f()` if `VirtualResult` is `void`, otherwise it must be a unary functor `f(result)` accepting the return value `result` as a parameter of type `VirtualResult const&` (to avoid extra copies of the return value, or of type `VirtualResult` or `VirtualResult const` if extra copies of the return value are irrelevant).

   Returns: | After postconditions have been specified, the object returned by this function allows to optionally specify exception guarantees.

2.     template<typename F> specify_nothing except(F const & f);

   Allow to specify exception guarantees.

   Parameters:

   `f`

   Nullary functor called by this library to check exception guarantees `f()`. Assertions within this functor are usually programmed using ``BOOST_CONTRACT_ASSERT``, but any exception thrown by a call to this functor indicates a contract assertion failure (and will result in this library calling ``boost::contract::except_failure``). This functor should capture variables by (constant) references (to access the values they will have at function exit).

   Returns: | After exception guarantees have been specified, the object returned by this function does not allow to specify any additional contract.