basic_facade_builder::add_facadetemplate <facade F, bool WithUpwardConversion = false>
using add_facade = basic_facade_builder</* see below */>;
The alias template add_facade of basic_facade_builder<Cs, Rs, C> adds a facade type into the template parameters. It merges typename F::convention_types into Cs, typename F::reflection_types into Rs, and F::constraints into C. Optionally, it adds a convention for implicit upward conversion into Cs when WithUpwardConversion is true.
Adding a facade type that contains duplicated convention or reflection types already defined in Cs or Rs is well-defined and does not have side effects on build at either compile-time or runtime. By default, WithUpwardConversion is false, which guarantees minimal binary size in code generation. However, upward conversion is helpful when an API requires backward compatibility. Users can opt-in to this feature by specifying true as the second parameter of add_facade, at the cost of potentially a slightly larger binary size.
#include <iostream>
#include <unordered_map>
#include "proxy.h"
PRO_DEF_MEM_DISPATCH(MemSize, size);
PRO_DEF_MEM_DISPATCH(MemAt, at);
PRO_DEF_MEM_DISPATCH(MemEmplace, emplace);
struct Copyable : pro::facade_builder
::support_copy<pro::constraint_level::nontrivial>
::build {};
struct BasicContainer : pro::facade_builder
::add_convention<MemSize, std::size_t() const noexcept>
::build {};
struct StringDictionary : pro::facade_builder
::add_facade<BasicContainer>
::add_facade<Copyable>
::add_convention<MemAt, std::string(std::size_t key) const>
::build {};
struct MutableStringDictionary : pro::facade_builder
::add_facade<StringDictionary, true>
::add_convention<MemEmplace, void(std::size_t key, std::string value)>
::build {};
int main() {
pro::proxy<MutableStringDictionary> p1 =
pro::make_proxy<MutableStringDictionary, std::unordered_map<std::size_t, std::string>>();
std::cout << p1->size() << "\n"; // Prints "0"
try {
std::cout << p1->at(123) << "\n"; // No output because the expression throws
} catch (const std::out_of_range& e) {
std::cerr << e.what() << "\n"; // Prints error message
}
p1->emplace(123, "lalala");
auto p2 = p1; // Performs a deep copy
p2->emplace(456, "trivial");
pro::proxy<StringDictionary> p3 = std::move(p2); // Performs an upward conversion from an rvalue reference
std::cout << p1->size() << "\n"; // Prints "1"
std::cout << p1->at(123) << "\n"; // Prints "lalala"
std::cout << std::boolalpha << p2.has_value() << "\n"; // Prints "false" because it is moved
std::cout << p3->size() << "\n"; // Prints "2"
std::cout << p3->at(123) << "\n"; // Prints "lalala"
std::cout << p3->at(456) << "\n"; // Prints "trivial"
}