.TH G_COPY 2 "11 April 1991" "Demeter" "Demeter Software"

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

.SH SYNOPSIS

virtual Universal* Universal::
.I g_copy
()

.SH DESCRIPTION

.I g_copy
performs a deep copy of the object to which the message is sent and
returns the copy. This means that
.I g_copy
makes an instance of the class of the object.
.I g_copy
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.

.SH REDEFINITION
Since
.I g_copy
is a virtual function, it can be redefined at any user class. This
means that the user can change what
.I g_copy
returns as a copy of any object. As a technical consideration, making
.I g_copy
virtual allows to define it recursively and to give the termination
condition as a redefinition at the terminal classes DemIdent, DemNumber,
DemReal, DemString, and DemText.

.SH RETURN VALUES

.I g_copy
returns an object of the class of the object to which the message was
sent. However, the type returned by
.I g_copy
is
.I Universal*,
since
.I g_copy
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();
.br
iCompound = (Compound*)iCompound->g_parse("demeter-input");
.br

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

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

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

.SH REFERENCES 

.I User Manual for The C++ Demeter System
.br
Walter L. Hursch
.br
Northeastern University, 1993

.I The Annotated C++ Reference Manual
.br
Margaret A. Ellis and Bjarne Stroustrup
.br
Addison-Wesley, 1990

.I C++ Primer
.br
Stanley B. Lippman
.br
Addison-Wesley, 1989