C++ enforcing implementing a pure virtual method from a different inheritance hierarchy
I have a Parent class and two Child classes:
class Parent
{
};
class Child1: public Parent
{
};
class Child2 : public Parent
{
};
I would like a second class hierarchy, with class Cousin at the top of the hierarchy and subclasses called Cousin1, Cousin2 etc:
class Cousin
{
virtual void doUsefulWork() = 0;
};
class Cousin1 : public Cousin
{
virtual void doUsefulWork() override
{
// One behaviour
}
};
class Cousin2 : public Cousin
{
virtual void doUsefulWork() override
{
// A different behaviour
}
};
Each Child subclass MUST inherit a Cousin subclass, to have an implementation of doUsefulWork():
class Child1 : public Parent, Cousin1
{
// Has implementation of doUsefulWork() from Cousin1
};
How can I guard against the author of a Child subclass forgetting to inherit a Cousin subclass? I would like something which generates a compile time error.
Every Child subclass must have access to an implementation of doUsefulWork().
I was thinking of making Cousin inherit from Parent and defining the pure virtual doUsefulWork() in Parent, but then I would have complicated multiple inheritance issues in Child subclasses?
c++ inheritance polymorphism multiple-inheritance pure-virtual
asked Nov 28 '18 at 13:23
user997112user997112
10.1k28106220
|
show 9 more comments
I have a Parent class and two Child classes:
class Parent
{
};
class Child1: public Parent
{
};
class Child2 : public Parent
{
};
I would like a second class hierarchy, with class Cousin at the top of the hierarchy and subclasses called Cousin1, Cousin2 etc:
class Cousin
{
virtual void doUsefulWork() = 0;
};
class Cousin1 : public Cousin
{
virtual void doUsefulWork() override
{
// One behaviour
}
};
class Cousin2 : public Cousin
{
virtual void doUsefulWork() override
{
// A different behaviour
}
};
Each Child subclass MUST inherit a Cousin subclass, to have an implementation of doUsefulWork():
class Child1 : public Parent, Cousin1
{
// Has implementation of doUsefulWork() from Cousin1
};
How can I guard against the author of a Child subclass forgetting to inherit a Cousin subclass? I would like something which generates a compile time error.
Every Child subclass must have access to an implementation of doUsefulWork().
I was thinking of making Cousin inherit from Parent and defining the pure virtual doUsefulWork() in Parent, but then I would have complicated multiple inheritance issues in Child subclasses?
c++ inheritance polymorphism multiple-inheritance pure-virtual
asked Nov 28 '18 at 13:23
user997112user997112
10.1k28106220
I would do it the other way around and inheritParentfromCousin. This will at least generate a compile error if an author of aChildclass forgets to reimplementdoUsefulWork()or inherit from a class that has an implementation.
– dave
Nov 28 '18 at 13:28
Or vice versa,class Parent : public Cousin { ...will do the trick.
– Eljay
Nov 28 '18 at 13:28
2
i hope the names are just for the example here. Imho the "child-parent" analogon is one of the worst, asstruct Child : Parentactually means that everyChildis-aParent, no wonder that it causes confusion when OO is thaught like that
– user463035818
Nov 28 '18 at 13:28
I'm not sure whetherclass Parent: public Cousin {is such a good idea. Derivingclass Child1: public Parent, Cousin1 {would have the base classCousintwice (and that smells like the need of virtual inheritance...)
– Scheff
Nov 28 '18 at 13:32
What I don't understand:Child1accessed with a pointer toParentmakes the virtual methoddoUsefulWork()invisible. It's a pointer toCousinwhich is needed. If in turn,Child3is accidentally not derived from anyCousinXwith overriddendoUsefulWork(), assigning it to a pointer toCousinshould cause trouble. There is something subtle, I'm not yet aware of.
– Scheff
Nov 28 '18 at 13:37
|
show 9 more comments
I have a Parent class and two Child classes:
class Parent
{
};
class Child1: public Parent
{
};
class Child2 : public Parent
{
};
I would like a second class hierarchy, with class Cousin at the top of the hierarchy and subclasses called Cousin1, Cousin2 etc:
class Cousin
{
virtual void doUsefulWork() = 0;
};
class Cousin1 : public Cousin
{
virtual void doUsefulWork() override
{
// One behaviour
}
};
class Cousin2 : public Cousin
{
virtual void doUsefulWork() override
{
// A different behaviour
}
};
Each Child subclass MUST inherit a Cousin subclass, to have an implementation of doUsefulWork():
class Child1 : public Parent, Cousin1
{
// Has implementation of doUsefulWork() from Cousin1
};
How can I guard against the author of a Child subclass forgetting to inherit a Cousin subclass? I would like something which generates a compile time error.
Every Child subclass must have access to an implementation of doUsefulWork().
I was thinking of making Cousin inherit from Parent and defining the pure virtual doUsefulWork() in Parent, but then I would have complicated multiple inheritance issues in Child subclasses?
c++ inheritance polymorphism multiple-inheritance pure-virtual
asked Nov 28 '18 at 13:23
user997112user997112
10.1k28106220
I have a Parent class and two Child classes:
class Parent
{
};
class Child1: public Parent
{
};
class Child2 : public Parent
{
};
I would like a second class hierarchy, with class Cousin at the top of the hierarchy and subclasses called Cousin1, Cousin2 etc:
class Cousin
{
virtual void doUsefulWork() = 0;
};
class Cousin1 : public Cousin
{
virtual void doUsefulWork() override
{
// One behaviour
}
};
class Cousin2 : public Cousin
{
virtual void doUsefulWork() override
{
// A different behaviour
}
};
Each Child subclass MUST inherit a Cousin subclass, to have an implementation of doUsefulWork():
class Child1 : public Parent, Cousin1
{
// Has implementation of doUsefulWork() from Cousin1
};
How can I guard against the author of a Child subclass forgetting to inherit a Cousin subclass? I would like something which generates a compile time error.
Every Child subclass must have access to an implementation of doUsefulWork().
I was thinking of making Cousin inherit from Parent and defining the pure virtual doUsefulWork() in Parent, but then I would have complicated multiple inheritance issues in Child subclasses?
c++ inheritance polymorphism multiple-inheritance pure-virtual
c++ inheritance polymorphism multiple-inheritance pure-virtual
asked Nov 28 '18 at 13:23
user997112user997112
10.1k28106220
asked Nov 28 '18 at 13:23
user997112user997112
10.1k28106220
edited Nov 28 '18 at 13:31
user997112
asked Nov 28 '18 at 13:23
user997112user997112
10.1k28106220
asked Nov 28 '18 at 13:23
user997112user997112
10.1k28106220
asked Nov 28 '18 at 13:23
user997112user997112
10.1k28106220
10.1k28106220
I would do it the other way around and inheritParentfromCousin. This will at least generate a compile error if an author of aChildclass forgets to reimplementdoUsefulWork()or inherit from a class that has an implementation.
– dave
Nov 28 '18 at 13:28
Or vice versa,class Parent : public Cousin { ...will do the trick.
– Eljay
Nov 28 '18 at 13:28
2
i hope the names are just for the example here. Imho the "child-parent" analogon is one of the worst, asstruct Child : Parentactually means that everyChildis-aParent, no wonder that it causes confusion when OO is thaught like that
– user463035818
Nov 28 '18 at 13:28
I'm not sure whetherclass Parent: public Cousin {is such a good idea. Derivingclass Child1: public Parent, Cousin1 {would have the base classCousintwice (and that smells like the need of virtual inheritance...)
– Scheff
Nov 28 '18 at 13:32
What I don't understand:Child1accessed with a pointer toParentmakes the virtual methoddoUsefulWork()invisible. It's a pointer toCousinwhich is needed. If in turn,Child3is accidentally not derived from anyCousinXwith overriddendoUsefulWork(), assigning it to a pointer toCousinshould cause trouble. There is something subtle, I'm not yet aware of.
– Scheff
Nov 28 '18 at 13:37
|
show 9 more comments
I would do it the other way around and inheritParentfromCousin. This will at least generate a compile error if an author of aChildclass forgets to reimplementdoUsefulWork()or inherit from a class that has an implementation.
– dave
Nov 28 '18 at 13:28
Or vice versa,class Parent : public Cousin { ...will do the trick.
– Eljay
Nov 28 '18 at 13:28
2
i hope the names are just for the example here. Imho the "child-parent" analogon is one of the worst, asstruct Child : Parentactually means that everyChildis-aParent, no wonder that it causes confusion when OO is thaught like that
– user463035818
Nov 28 '18 at 13:28
I'm not sure whetherclass Parent: public Cousin {is such a good idea. Derivingclass Child1: public Parent, Cousin1 {would have the base classCousintwice (and that smells like the need of virtual inheritance...)
– Scheff
Nov 28 '18 at 13:32
What I don't understand:Child1accessed with a pointer toParentmakes the virtual methoddoUsefulWork()invisible. It's a pointer toCousinwhich is needed. If in turn,Child3is accidentally not derived from anyCousinXwith overriddendoUsefulWork(), assigning it to a pointer toCousinshould cause trouble. There is something subtle, I'm not yet aware of.
– Scheff
Nov 28 '18 at 13:37
I would do it the other way around and inherit
Parent from Cousin. This will at least generate a compile error if an author of a Child class forgets to reimplement doUsefulWork() or inherit from a class that has an implementation.– dave
Nov 28 '18 at 13:28
I would do it the other way around and inherit
Parent from Cousin. This will at least generate a compile error if an author of a Child class forgets to reimplement doUsefulWork() or inherit from a class that has an implementation.– dave
Nov 28 '18 at 13:28
Or vice versa,
class Parent : public Cousin { ... will do the trick.– Eljay
Nov 28 '18 at 13:28
Or vice versa,
class Parent : public Cousin { ... will do the trick.– Eljay
Nov 28 '18 at 13:28
2
2
i hope the names are just for the example here. Imho the "child-parent" analogon is one of the worst, as
struct Child : Parent actually means that every Child is-a Parent, no wonder that it causes confusion when OO is thaught like that– user463035818
Nov 28 '18 at 13:28
i hope the names are just for the example here. Imho the "child-parent" analogon is one of the worst, as
struct Child : Parent actually means that every Child is-a Parent, no wonder that it causes confusion when OO is thaught like that– user463035818
Nov 28 '18 at 13:28
I'm not sure whether
class Parent: public Cousin { is such a good idea. Deriving class Child1: public Parent, Cousin1 { would have the base class Cousin twice (and that smells like the need of virtual inheritance...)– Scheff
Nov 28 '18 at 13:32
I'm not sure whether
class Parent: public Cousin { is such a good idea. Deriving class Child1: public Parent, Cousin1 { would have the base class Cousin twice (and that smells like the need of virtual inheritance...)– Scheff
Nov 28 '18 at 13:32
What I don't understand:
Child1 accessed with a pointer to Parent makes the virtual method doUsefulWork() invisible. It's a pointer to Cousin which is needed. If in turn, Child3 is accidentally not derived from any CousinX with overridden doUsefulWork(), assigning it to a pointer to Cousin should cause trouble. There is something subtle, I'm not yet aware of.– Scheff
Nov 28 '18 at 13:37
What I don't understand:
Child1 accessed with a pointer to Parent makes the virtual method doUsefulWork() invisible. It's a pointer to Cousin which is needed. If in turn, Child3 is accidentally not derived from any CousinX with overridden doUsefulWork(), assigning it to a pointer to Cousin should cause trouble. There is something subtle, I'm not yet aware of.– Scheff
Nov 28 '18 at 13:37
|
show 9 more comments
1 Answer
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How can I guard against the author of a Child subclass forgetting to inherit a Cousin subclass? I would like something which generates a compile time error.
The reason you are implementing these interfaces is because there must be functions that consume these interfaces. If an object doesn't implement the interface you get a compiler error when passing the object to that function - that acts as an enforcing check that the object must implement that interface.
answered Nov 28 '18 at 13:43
Maxim EgorushkinMaxim Egorushkin
89.2k11104191
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How can I guard against the author of a Child subclass forgetting to inherit a Cousin subclass? I would like something which generates a compile time error.
The reason you are implementing these interfaces is because there must be functions that consume these interfaces. If an object doesn't implement the interface you get a compiler error when passing the object to that function - that acts as an enforcing check that the object must implement that interface.
answered Nov 28 '18 at 13:43
Maxim EgorushkinMaxim Egorushkin
89.2k11104191
add a comment |
How can I guard against the author of a Child subclass forgetting to inherit a Cousin subclass? I would like something which generates a compile time error.
The reason you are implementing these interfaces is because there must be functions that consume these interfaces. If an object doesn't implement the interface you get a compiler error when passing the object to that function - that acts as an enforcing check that the object must implement that interface.
answered Nov 28 '18 at 13:43
Maxim EgorushkinMaxim Egorushkin
89.2k11104191
add a comment |
How can I guard against the author of a Child subclass forgetting to inherit a Cousin subclass? I would like something which generates a compile time error.
The reason you are implementing these interfaces is because there must be functions that consume these interfaces. If an object doesn't implement the interface you get a compiler error when passing the object to that function - that acts as an enforcing check that the object must implement that interface.
answered Nov 28 '18 at 13:43
Maxim EgorushkinMaxim Egorushkin
89.2k11104191
How can I guard against the author of a Child subclass forgetting to inherit a Cousin subclass? I would like something which generates a compile time error.
The reason you are implementing these interfaces is because there must be functions that consume these interfaces. If an object doesn't implement the interface you get a compiler error when passing the object to that function - that acts as an enforcing check that the object must implement that interface.
answered Nov 28 '18 at 13:43
Maxim EgorushkinMaxim Egorushkin
89.2k11104191
answered Nov 28 '18 at 13:43
Maxim EgorushkinMaxim Egorushkin
89.2k11104191
answered Nov 28 '18 at 13:43
Maxim EgorushkinMaxim Egorushkin
89.2k11104191
answered Nov 28 '18 at 13:43
Maxim EgorushkinMaxim Egorushkin
89.2k11104191
89.2k11104191
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I would do it the other way around and inherit
ParentfromCousin. This will at least generate a compile error if an author of aChildclass forgets to reimplementdoUsefulWork()or inherit from a class that has an implementation.– dave
Nov 28 '18 at 13:28
Or vice versa,
class Parent : public Cousin { ...will do the trick.– Eljay
Nov 28 '18 at 13:28
2
i hope the names are just for the example here. Imho the "child-parent" analogon is one of the worst, as
struct Child : Parentactually means that everyChildis-aParent, no wonder that it causes confusion when OO is thaught like that– user463035818
Nov 28 '18 at 13:28
I'm not sure whether
class Parent: public Cousin {is such a good idea. Derivingclass Child1: public Parent, Cousin1 {would have the base classCousintwice (and that smells like the need of virtual inheritance...)– Scheff
Nov 28 '18 at 13:32
What I don't understand:
Child1accessed with a pointer toParentmakes the virtual methoddoUsefulWork()invisible. It's a pointer toCousinwhich is needed. If in turn,Child3is accidentally not derived from anyCousinXwith overriddendoUsefulWork(), assigning it to a pointer toCousinshould cause trouble. There is something subtle, I'm not yet aware of.– Scheff
Nov 28 '18 at 13:37