Customize the application output
**************************************************

In the previous tutorials, we considered applications that return scalar values as output, such as:

.. code-block:: cpp

    HUX_DECLARE_PROCESSING(app_output, input_channel, {
        
        float acc_x = ... ;

        HUX_DECLARE_OUTPUT_VALUE(result, Float, "acc_x", acc_x);
        return result;
    });
    
    HUX_REGISTER_OUTPUT(app_output);

which produces a simulation output of the following form:

.. code-block:: txt

    {
        "acc_x":0.23
    }

    {
        "acc_x":0.12
    }
    ...

Overall, the :c:macro:`HUX_DECLARE_OUTPUT_VALUE` construct supports the following scalar schemas:

 - **Float**: an output whose value is of C++ type *float*
 - **Double**: an output whose value is of C++ type *double*
 - **Integer**: an output whose value is of type :cpp:member:`hux::int32_t`
 - **Long**: an output whose value is of type :cpp:member:`hux::int64_t`
 - **Boolean**: an output whose value is of C++ type *bool*
 - **String**: an output whose value is of type :cpp:member:`hux::string`

However, in many contexts, an application might need to return more than a single field.
For this purpose, the :c:macro:`HUX_DECLARE_OUTPUT_VALUE` construct allows to declare output values having **Object** schema.
An output value with **Object** schema is a container for one or more output values.
As an example, we could output the X, Y and Z accelerations from an inertial sensor:

.. code-block:: cpp

    HUX_DECLARE_PROCESSING(app_output, input_channel, {
        
        float acc_x = ... ;
        float acc_y = ... ;
        float acc_z = ... ;

        HUX_DECLARE_OUTPUT_VALUE(x_out, Float, "x", acc_x);
        HUX_DECLARE_OUTPUT_VALUE(y_out, Float, "y", acc_y);
        HUX_DECLARE_OUTPUT_VALUE(z_out, Float, "z", acc_z);

        HUX_DECLARE_OUTPUT_VALUE(xyz_out, Object, "acceleration", x_out, y_out, z_out);

        return xyz_out;
    });
    
    HUX_REGISTER_OUTPUT(app_output);

which produces an output of the following form:

.. code-block:: txt

    {
        "acceleration":{
            "x":0.26,
            "y":0.11,
            "z":-1.01
        }
    }

    {
        "acceleration":{
            "x":0.25,
            "y":0.17,
            "z":0.98
        }
    }
    ...

It is also possible to include an output value having **Object** schema within another output value with **Object** schema:

.. code-block:: cpp

    HUX_DECLARE_PROCESSING(app_output, input_channel, {
        
        float acc_x = ... ;
        float acc_y = ... ;
        float acc_z = ... ;

        bool alarm_active = ... ;
        hux::uint64_t alarm_ts = ... ; 

        HUX_DECLARE_OUTPUT_VALUE(x_out, Float, "x", acc_x);
        HUX_DECLARE_OUTPUT_VALUE(y_out, Float, "y", acc_y);
        HUX_DECLARE_OUTPUT_VALUE(z_out, Float, "z", acc_z);
        HUX_DECLARE_OUTPUT_VALUE(xyz_out, Object, "acceleration", x_out, y_out, z_out);

        HUX_DECLARE_OUTPUT_VALUE(alarm_active_out, Boolean, "active", alarm_active);
        HUX_DECLARE_OUTPUT_VALUE(alarm_ts_out, Long, "timestamp", alarm_ts);
        HUX_DECLARE_OUTPUT_VALUE(alarm_out, Object, "alarm", alarm_active_out, alarm_ts_out);

        HUX_DECLARE_OUTPUT_VALUE(monitoring_out, Object, "monitoring", xyz_out, alarm_out);

        return monitoring_out;
    });
    
    HUX_REGISTER_OUTPUT(app_output);

which produces an output of the following form:

.. code-block:: txt

    {
        "monitoring":{
            "acceleration":{
                "x":0.25,
                "y":0.11,
                "z":1.01
            },
            "alarm":{
                "active":true,
                "timestamp":1656955471200
            }
        }
    }
    ...