Static Polymorphism

Using compile time techniques to grant PolymorphicBehaviour at CompileTime , as opposed to RunTime.

A CeePlusPlus example follows:

template
class base : public impl {
public: void op() { impl::op(); }};
struct impl { void op() { /* work here */ }};
base().op();


Typically StaticPolymorphism surfaces as implementation in the form of the CuriouslyRecurringTemplatePattern.

If you wish to define base as in terms of an abstract base class, and hold a collection, with differing implementations:

#include
#include
class virtual_base {
public: virtual void dynamic_op() = 0; };
template
class base : public impl,
public virtual_base {
public: void dynamic_op() { impl::op(); }};
struct impl_1 { void op() { std::cout << "impl_1" << std::endl; }};
struct impl_2 { void op() { std::cout << "impl_2" << std::endl; }};
typedef std::vector > bv;
void main() {
bv vector_;
vector_.push_back(new base());
vector_.push_back(new base());
for (bv::iterator item_(vector_.begin()); item_ != vector_.end(); (*item_++)->dynamic_op()){}
}


However, std::vector > isn't a good thing. And main() should return int...

---

Equivalent code in OcamlLanguage:

type base = unit -> unit
let impl1 : base = fun () -> print_endline "impl_1"
let impl2 : base = fun () -> print_endline "impl_2"
let _tmain () =
let c_vector = [impl1, impl2] in
List.iter (fun c_current -> c_current ()) c_vector


If you need many statically polymorphic methods on "base", you have to model it as a record / object instead of a function. -- PanuKalliokoski

Can you give an example?

---

A C Example:

The Microsoft Windows API uses compile switches to select between 8 bit ASCII and wide characters. This was done by naming the basic interface calls something like FooA and FooW and then use a compile switch and a #define statement to map Foo to either FooA or FooW.

An attempt to recreate the initial example with this technique.

// Possible Method Choices

#if defined(USE_A)

#define op opA


#endif

#if defined(USE_B)

#define op opB


#endif

#if defined(USE_C)

#define op opC


#endif