Given:
namespace A {
class Foo;
class Bar;
}
namespace B {
class Foo;
class Bar;
}
I want to template a class on the namespace A or B such that the following works:
template<name> class C {
name::Foo* foo;
name::Bar* bar;
}
Can this be done directly or do I need to create a pair of struct types with typedefs in them?
You can't template on a namespace. If you're able to use a class (with most likely public attributes/static methods) then you can template on the class as a semi-workaround.
With my limited knowledge, I believe that this would be a useful tool, and seems to be a relationship that could exist between namespaces and templates. Some people argue that it would be hard to implement and is unnecessary, however.
In the example above, I would use structs rather than namespaces (I use struct over class because by default its access is "public"). Below should be a fully compilable example:
#include <iostream>
// Replaces namepace 'A' from above.
templates
struct Option1 {
class Foo;
//Example function, too.
void myFunc() {
std::cout << "Hello!\n";
}
};
// A second Option for example.
struct Option2 {
class Foo;
void myFunc() {
std::cout << "Hola!!\n";
}
};
// Can be in .cpp file
class Option1::Foo {
public:
Foo() { display(); }
void display() {
std::cout << "Option 1.\n";
}
};
class Option2::Foo {
public:
Foo() { display(); }
void display() {
std::cout << "Option 2.\n";
}
};
The template could then be as follows:
// The typename C would need class 'Foo'
template <typename C>
class OptionSelect : public C
{
typename C::Foo* foo;
public:
OptionSelect() {
foo = new typename C::Foo();
}
};
int main() {
OptionSelect<Option1> opt1;
OptionSelect<Option2> opt2;
opt1.myFunc(); // Provided that template had myFunc
opt2.myFunc();
return 0;
}
The result should be as follows when built:
Option 1.
Option 2.
Hello!
Hola!!
I got the idea of inheriting a template class from here, though I'll admit without defining myFunc() as I did, inheriting the template would be optional. The article is worth checking out. It has many useful and unconventional tricks to using templates.
