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Posted to issues@mesos.apache.org by "Benjamin Hindman (JIRA)" <ji...@apache.org> on 2015/06/20 19:34:00 UTC
[jira] [Commented] (MESOS-2756) Update style guide: Avoid object
slicing
[ https://issues.apache.org/jira/browse/MESOS-2756?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14594699#comment-14594699 ]
Benjamin Hindman commented on MESOS-2756:
-----------------------------------------
While I agree that we should disallow instantiation of the base class if we don't want people to be constructing those objects, I don't understand how disallowing instantiation of the base class helps with object slicing. Making the "disallow construction of base class" modifications to your example still results in the object slicing problem:
{code:title=ObjectSlicing.cpp|borderStyle=solid}
#include <stdio.h>
#include <vector>
class Base {
protected:
Base() {}
Base(int _v) : v(_v) {}
public:
virtual int get() const { return v; }
protected:
int v;
};
class Derived : public Base {
public:
Derived(int _v) : Base(_v) {}
virtual int get() const { return v + 1; }
};
int main() {
// Base b(5);
Derived d(5);
std::vector<Base> vec;
// vec.push_back(b);
vec.push_back(d);
for (const auto& v : vec) {
printf("[%d]\n", v.get());
}
}
{code}
> Update style guide: Avoid object slicing
> ----------------------------------------
>
> Key: MESOS-2756
> URL: https://issues.apache.org/jira/browse/MESOS-2756
> Project: Mesos
> Issue Type: Improvement
> Reporter: Joris Van Remoortere
> Assignee: Joris Van Remoortere
> Labels: c++
>
> In order to improve the safety of our code base, let's augment the style guide to:
> "Disallow public construction of base classes"
> so that we can avoid the object slicing problem. This is a good pattern to follow in general as it prevents subtle semantic bugs like the following:
> {code:title=ObjectSlicing.cpp|borderStyle=solid}
> #include <stdio.h>
> #include <vector>
> class Base {
> public:
> Base(int _v) : v(_v) {}
> virtual int get() const { return v; }
> protected:
> int v;
> };
> class Derived : public Base {
> public:
> Derived(int _v) : Base(_v) {}
> virtual int get() const { return v + 1; }
> };
> int main() {
> Base b(5);
> Derived d(5);
> std::vector<Base> vec;
> vec.push_back(b);
> vec.push_back(d);
> for (const auto& v : vec) {
> printf("[%d]\n", v.get());
> }
> }
> {code}
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