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Answer Posted / chris pearson
"Object slicing" is an informal term that is often used (as
in all the answers above) to indicate that (in some
languages, usually C++) assignment to a superclass instance
from a subclass instance does not copy the member variables
defined only in the subclass.
This usage of the term is inapt and misleading, for several
reasons:
1. The notion that an object has been damaged ("sliced")
suggests something to be avoided. However, it is not
possible (or meaningful) in any statically typed language
for a superclass instance to contain subclass member
variables, so in fact assignment to a superclass operates
correctly and is a useful language feature.
2. After such an assignment, the source, subclass, object
remains unchanged, so it has in no sense been been "sliced".
3. After such an assignment, all member variables of the
destination, superclass, object are present and have been
assigned values, so neither has it in any sense
been "sliced".
The case to which the term "object slicing" is better
applied is more subtle and problematic. It occurs in a
statically typed language such as C++ where assignment
appears to be to a superclass instance but is actually to a
subclass instance.
For example:
void myassign(mysuperclass &dest)
{
mysuperclass source;
dest = source;
}
mysubclass sub;
myassign(sub); // assigns only superclass members of
sub!
A better term for this case might be "partial assignment".
Such partial assignment is not possible in Java because
that language only allows object references, and assignment
to a reference simply causes it to refer to a different
object.
-- Chris
| Is This Answer Correct ? | 9 Yes | 2 No |
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