Using compile time techniques to grant PolymorphicBehaviour at CompileTime , as opposed to RunTime.
A CeePlusPlus example follows:
template <class impl>
class base : public impl {
public: void op() { impl::op(); },},;
struct impl { void op() { /* work here */ },},;
base<impl>().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 <iostream>
#include <vector>
class virtual_base {
public: virtual void dynamic_op() = 0; },;
template <class impl>
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<std::auto_ptr<virtual_base> > bv;
void main() {
bv vector_;
vector_.push_back(new base<impl_1>());
vector_.push_back(new base<impl_2>());
for (bv::iterator item_(vector_.begin()); item_ != vector_.end(); (*item_++)->dynamic_op()){},
},
However, std::vector<std::auto_ptr<T> > 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