basic_facade_builder::add_convention, basic_facade_builder::add_direct_convention, basic_facade_builder::add_indirect_conventiontemplate <class D, class... Os> requires(/* see below */)
using add_convention = add_indirect_convention<D, Os...>;
template <class D, class... Os> requires(/* see below */)
using add_indirect_convention = basic_facade_builder</* see below */>;
template <class D, class... Os> requires(/* see below */)
using add_direct_convention = basic_facade_builder</* see below */>;
The alias templates add_convention, add_indirect_convention, and add_direct_convention of basic_facade_builder<Cs, Rs, C> add convention types to the template parameters. The expression inside requires is equivalent to sizeof...(Os) > 0u and each type in Os meets the ProOverload requirements. Let F be a facade type,
add_convention is equivalent to add_indirect_convention.add_indirect_convention merges an implementation-defined convention type IC into Cs, where:
IC::is_direct is false.typename IC::dispatch_type is D.typename IC::overload_types is a tuple-like type of distinct types in Os.typename IC::template accessor<F> is typename D::template accessor<F, IC, Os...>.add_direct_convention merges an implementation-defined convention type IC into Cs, where:
IC::is_direct is true.typename IC::dispatch_type is D.typename IC::overload_types is a tuple-like type of distinct types in Os.typename IC::template accessor<F> is typename D::template accessor<F, IC, Os...>.When Cs already contains a convention type IC2 where IC2::is_direct == IC::is_direct && std::is_same_v<typename IC2::dispatch_type, typename IC::dispatch_type> is true, Os merges with typename IC2::overload_types and removes duplicates, and std::tuple_size_v<Cs> shall not change.
Adding duplicated combinations of some dispatch type and overload type is well-defined (either directly via add_convention, add_indirect_convention, add_direct_convention, or indirectly via add_facade), and does not have side-effects to build at either compile-time or runtime.
#include <iostream>
#include <memory>
#include <string>
#include "proxy.h"
PRO_DEF_FREE_DISPATCH(FreeToString, std::to_string, ToString);
struct BasicStringable : pro::facade_builder
::add_convention<FreeToString, std::string() const>
::build {};
struct Stringable : pro::facade_builder
::add_facade<BasicStringable>
::support_copy<pro::constraint_level::nontrivial>
::add_direct_convention<pro::conversion_dispatch<pro::proxy<BasicStringable>>,
pro::proxy<BasicStringable>() &&>
::build {};
int main() {
pro::proxy<Stringable> p1 = std::make_shared<int>(123);
pro::proxy<Stringable> p2 = p1;
pro::proxy<BasicStringable> p3 = static_cast<pro::proxy<BasicStringable>>(std::move(p2));
pro::proxy<BasicStringable> p4 = std::move(p3);
// pro::proxy<BasicStringable> p5 = p4; // Won't compile
std::cout << ToString(*p4) << "\n"; // Prints: "123"
std::cout << std::boolalpha << p3.has_value() << "\n"; // Prints: "false"
}