Re: Class hierarchies and concepts
On Dec 15, 12:22 am, kelvSYC <kelv...@gmail.com> wrote:
Suppose I have a class hierarchy, whose root class is Foo. Is there a
way to formally prescribe that subclasses of Foo has to export a
type? That is:
class Foo { // abstract base class
// Subclasses must export a type BarType, possibly with a
consistent interface - none exists for Foo itself
};
struct Foo1 : public Foo {
typedef ... BarType;
};
struct Foo2 : public Foo {
struct BarType { ... };
};
// So Foo1::BarType and FooType::BarType are valid, and Foo::BarType
could be any of these two
If such a thing exists, is it possible to declare an abstract method
in Foo that returns BarType (where subclasses return their own
BarType)?
And how would you call such an abstract method?
Foo* f = obtainFoo1or2();
auto ret = f->someAbstractMethod();
then 'ret' will be of what type?
If not, is there a good workaround?
Use templates. You can use your "deriving types" as
types used to specialize a template and you can then
refer to some type defined inside it. For example:
template <class InFoo>
struct Foo
{
typename InFoo::BarType someAbstractMethod() ...
};
Regards,
Sektor
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