basic_facade_builder::restrict_layouttemplate <std::size_t PtrSize, std::size_t PtrAlign = /* see below */>
requires(std::has_single_bit(PtrAlign) && PtrSize % PtrAlign == 0u)
using restrict_layout = basic_facade_builder</* see below */>;
The alias template restrict_layout of basic_facade_builder<Cs, Rs, C> adds layout restrictions to the template parameters, specifically C::max_size and C::max_align. The default value of PtrAlign is the maximum possible alignment of an object of size PtrSize, not greater than alignof(std::max_align_t). After applying the restriction, C::max_size becomes std::min(C::max_size, PtrSize), and C::max_align becomes std::min(C::max_align, PtrAlign).
If no layout restriction is applied before specifying build, the default value of build::constraints.max_size is sizeof(void*) * 2, and the default value of build::constraints.max_align is alignof(void*).
#include <array>
#include <memory>
#include "proxy.h"
struct DefaultFacade : pro::facade_builder::build {};
struct SmallFacade : pro::facade_builder
::restrict_layout<sizeof(void*)>
::build {};
int main() {
static_assert(sizeof(pro::proxy<DefaultFacade>) > sizeof(pro::proxy<SmallFacade>));
static_assert(pro::proxiable<std::unique_ptr<int>, DefaultFacade>);
static_assert(pro::proxiable<std::unique_ptr<int>, SmallFacade>);
static_assert(pro::proxiable<std::shared_ptr<int>, DefaultFacade>);
static_assert(!pro::proxiable<std::shared_ptr<int>, SmallFacade>);
static_assert(pro::inplace_proxiable_target<std::array<int*, 2>, DefaultFacade>);
static_assert(!pro::inplace_proxiable_target<std::array<int*, 2>, SmallFacade>);
static_assert(!pro::inplace_proxiable_target<std::array<int*, 3>, DefaultFacade>);
static_assert(!pro::inplace_proxiable_target<std::array<int*, 3>, SmallFacade>);
pro::proxy<DefaultFacade> p1 = std::make_shared<int>(123);
// pro::proxy<SmallFacade> p2 = std::make_shared<int>(123); // Won't compile
}