Static Polymorphism

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...

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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?

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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