G_COPY(2)               Demeter Software                G_COPY(2)



NAME
     g_copy - sends the generic copy message to an object.


SYNOPSIS
     virtual Universal* Universal:: _g__c_o_p_y ()


DESCRIPTION
     _g__c_o_p_y performs a deep copy of the object to which the  mes-
     sage  is  sent  and returns the copy. This means that _g__c_o_p_y
     makes an instance of the class of  the  object.   _g__c_o_p_y  is
     then  sent recursively to each part of the object to fill in
     the corresponding part  in  the  newly  made  instance.  The
     receiving  object  must be a tree object. That is, it cannot
     have any cycles or shared subobjects.


REDEFINITION
     Since _g__c_o_p_y is a virtual function, it can be  redefined  at
     any  user  class.  This  means that the user can change what
     _g__c_o_p_y returns as a copy of any object. As a technical  con-
     sideration, making _g__c_o_p_y virtual allows to define it recur-
     sively and to give the termination condition as a  redefini-
     tion  at  the terminal classes DemIdent, DemNumber, DemReal,
     DemString, and DemText.


RETURN VALUES
     _g__c_o_p_y returns an object of the class of the object to which
     the  message  was sent. However, the type returned by _g__c_o_p_y
     is _U_n_i_v_e_r_s_a_l*, since _g__c_o_p_y does not know in advance to what
     class  the message is going to be sent. Therefore, the value
     returned must be cast to the appropriate type before it  can
     be assigned or used in any way. For example:

     Compound* iCompound = new Compound();
     iCompound = (Compound*)iCompound->g_parse("demeter-input");

     Compound* iCompound2 = (Compound*)iCompound->g_copy();

     if( iCompound->g_equal( iCompound2 ) == 1 )
        cout << "Copied and original are equal\n";
     else
        cout << "Copied and original are NOT equal\n";


SEE ALSO
     g_parse(2), g_equal(2), terminal(2), g_code(2), g_delete(2)






Demeter            Last change: 11 April 1991                   1






G_COPY(2)               Demeter Software                G_COPY(2)



REFERENCES
     _U_s_e_r _M_a_n_u_a_l _f_o_r _T_h_e _C++ _D_e_m_e_t_e_r
     Walter L. Hursch
     Northeastern University, 1993

     _T_h_e _A_n_n_o_t_a_t_e_d _C++ _R_e_f_e_r_e_n_c_e _M_a_n_u_a_l
     Margaret A. Ellis and Bjarne Stroustrup
     Addison-Wesley, 1990

     _C++ _P_r_i_m_e_r
     Stanley B. Lippman
     Addison-Wesley, 1989











































Demeter            Last change: 11 April 1991                   2