Why not split the processing objects in C++?
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ES.63: do not split processing objects
Reason (reason)
Segmentation means that the assignment or initialization of an object is only part of the object-- in most cases, it results in an error, because the object is intended to be processed as a whole. In rare cases, you do need to split up, but such code can be difficult to understand.
Example (sample)
Class Shape {/ *... * /}
Class Circle: public Shape {/ *... * / Point c; int r;}
Circle c {{0, 0}, 42}
Shape s {c}; / / copy construct only the Shape part of Circle
S = c; / / or copy assign only the Shape part of Circle
Void assign (const Shape& src, Shape& dest) {
Dest = src
}
Circle c2 {{1, 1}, 43}
Assign (c, c2); / / oops, not the whole state is transferred
Assert (c = = c2); / / if we supply copying, we should also provide comparison
/ / but this will likely return false
Because the center and radius are not copied from c to s, it produces meaningless results. The first protection forbids the assignment of the base class.
Alternative (optional)
If you do need to split the processing object, define an explicit operation to accomplish this function. This can avoid readers' confusion. For example:
Class Smiley: public Circle {
Public:
Circle copy_circle ()
/ /...
}
Smiley sm {/ *... * /}
Circle C1 {sm}; / / ideally prevented by the definition of Circle
Circle c2 {sm.copy_circle ()}; Enforcement (implementation recommendation)
Warn against slicing.
The split process is found to issue a warning.
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