The generic interface for material properties generates functions matching the following prototype:

mfront_gmp_real (*)(mfront_gmp_OutputStatus* const,       // output status
const mfront_gmp_real* const,         // arguments
const mfront_gmp_size_type,           // number of arguments
const mfront_gmp_OutOfBoundsPolicy);  // out of bounds policy

The mfront_gmp_OutputStatus structure and the mfront_gmp_OutOfBoundsPolicy enumeration type are described in the next paragraphs.

The arguments are passed using a continuous array. The number of arguments is used to make some basic consistency checks. The list of arguments can be retrieved using the ExternalLibraryManager class (See Section @???).

If the material property declares parameters (and that the parameters_as_static_variables DSL option was not specified), their names and default values can be retrieved using the ExternalLibraryManager class. The value of those parameters can also be modified using the ExternalLibraryManager class (See Section @???).

Note: link with the cyrano interface for material properties

The generic interface for material properties is very similar to the cyrano interface. In pratice, both interfaces shares a common base class (called GenericMaterialPropertyInterfaceBase).

### The mfront_gmp_OutputStatus structure

The mfront_gmp_OutputStatus structure describes the output status of the evaluation of a material property.

This data structure is defined as follows:

/*!
* \brief this structure summarizes the exit status of a function conforming to
* one of the generic material property interface.
*/
typedef struct {
/*!
* \brief exit status
*
* The exit status is zero if the result has been correctly evaluated.
*
* If the exit status is 1, a result has been computed, but it must be used
* with caution. This is typically used to report that one argument was out of
* its bounds.
*
* All negative values indicates that the result is not usable. For a material
* property, thereturned is nan.
*
* For a material property, a negative value has the following meaning:
*
* - If the exit status is -1, an argument was out of its physical bounds, or
*   out of its bounds and a strict out of bounds policy is declared.
* - If the exit status is -2, a C++ exception was thrown. If the exception
*   was a child of std::exception, the content of the string returned by
*   the what method is copyied in the message field. Otherwise, the
*   message field contains the "unknown exception" string.
* - If the exit status is -3, an error occured in the C library, i.e. the
*   errno value was set to a non zero value during the computation.
*   The value of errno corresponding to the error is stored to in the
*   c_error_number field of this structure. The string returned by
*   strerrno is returned. Note that the errno value is always reset to
*   the  value it had before the call.
* - If the exit status is -4, the computed value is invalid (either \nan,
*   inf, or -inf).
* - If the exit status is -5, the number of arguments is invalid.
*/
int status;
//! \brief error number reported by the C library.
int c_error_number;
/*!
* \brief bounds status
* This status has the following meaning:
* - zero means that no argument was outside its bounds or its physical
* bounds.
* - a negative values means that one argument went beyond its physical
* bounds.
*   The absolute value gives the rank of this argument (here the rank starts
* at 1).
* - a positive value means that one argument went beyond its bounds.
*   The value gives the rank of this argument (here the rank starts at 1).
*/
int bounds_status;
//! \brief error message
char msg[512];
} mfront_gmp_OutputStatus;  // end of struct mfront_gmp_OutputStatus

### The mfront_gmp_OutOfBoundsPolicy enumeration type

The mfront_gmp_OutOfBoundsPolicy enumeration type is defined as follows:

/*!
* \brief available out of bounds policies
*/
typedef enum {
GENERIC_MATERIALPROPERTY_NONE_POLICY,    /*!<
* With this policy, nothing is done if
* the arguments are    out of their
* bounds    (checks are not even
* performed).
*/
GENERIC_MATERIALPROPERTY_WARNING_POLICY, /*!<
* With this policy, checks on the
* arguments are performed. If one
* argument if out of its bounds,
* this will be reported in the
* output status and an
* appropriate error message will be
* reported. The computations are
* however performed.
*/
GENERIC_MATERIALPROPERTY_STRICT_POLICY   /*!<
* With this policy, checks on the
* arguments are   performed. If one
* argument   if out of its bounds,
* this   will be reported in the
* output   status and an   appropriate
* error   message will be reported.
*/
} mfront_gmp_OutOfBoundsPolicy;  // end of mfront_gmp_OutOfBoundsPolicy`