xo-umbrella2/include/reflect/StructReflector.hpp

/* @file StructReflector.hpp */

#pragma once

#include "reflect/Reflect.hpp"
#include "reflect/TypeDescr.hpp"
#include "reflect/struct/StructMember.hpp"
#include "reflect/struct/StructTdx.hpp"
#include <vector>

namespace xo {
  namespace reflect {
    template<typename StructT, bool IsSelfTaggingDescendant>
    class SelfTagger {};

    template<typename StructT>
    struct SelfTagger<StructT, true> {
      static TaggedPtr self_tp(void * object) {
	return (reinterpret_cast<StructT *>(object))->self_tp();
      }
    };

    template<typename StructT>
    struct SelfTagger<StructT, false> {
      static TaggedPtr self_tp(void * /*object*/) { assert(false); return TaggedPtr::universal_null(); }
    };

    /* RAII pattern for reflecting a struct.
     *
     * Use:
     *   struct Foo { int x_; double y_; };
     *
     *   StructReflector<Foo> sr;
     *   REFLECT_LITERAL_MEMBER(sr, x_);
     *   REFLECT_LITERAL_MEMBER(sr, y_);
     *
     *   // optional: regardless, reflection will be completed when sr goes out of scope
     *   sr.require_complete(); 
     */
    template<typename StructT>
    class StructReflector {
    public:
      using struct_t = StructT;

    public:
      StructReflector() : td_{EstablishTypeDescr::establish<StructT>()} {}
      ~StructReflector() {
	this->require_complete();
      }
      
      bool is_complete() const { return s_reflected_flag; }
      bool is_incomplete() const { return !s_reflected_flag; }

      template<typename OwnerT, typename MemberT>
      void reflect_member(std::string const & member_name,
			  MemberT OwnerT::* member_addr) {

	auto accessor
	  (GeneralStructMemberAccessor<StructT, OwnerT, MemberT>::make(member_addr));

	/* used to do this in GeneralStructMemberAccessor<> ctor,
	 * but that introduces #include cycle
	 */
	Reflect::require<MemberT>();

	this->member_v_.emplace_back(member_name, std::move(accessor));
      } /*reflect_member*/

      void require_complete() {
	if(!s_reflected_flag) {
	  s_reflected_flag = true;

	  constexpr bool have_to_self_tp = std::is_base_of_v<SelfTagging, StructT>;

	  /* if self-tagging,  can use .self_tp() to get most-derived tagged pointer */
	  auto to_self_tp_fn
	    = ([](void * object)
	    {
	      return SelfTagger<StructT, have_to_self_tp>::self_tp(object);
	    });

	  auto tdx = StructTdx::make(std::move(this->member_v_),
				     have_to_self_tp,
				     to_self_tp_fn);

	  this->td_->assign_tdextra(std::move(tdx));
	}
      } /*complete*/
      
      template<typename AncestorT>
      void adopt_ancestors() {
	assert(Reflect::is_reflected<AncestorT>());

	TypeDescr ancestor_td = Reflect::require<AncestorT>();

	/* requires that reflection of AncestorT has completed */
	{
	  assert(ancestor_td->is_struct());
	  assert(ancestor_td->complete_flag());
	}

	/* for structs,
	 * we know that object argument to TypeDescr::n_child() is unused
	 */
	for (uint32_t i = 0, n = ancestor_td->n_child(nullptr); i < n; ++i) {
	  StructMember const & member = ancestor_td->struct_member(i);

	  this->member_v_.push_back(member.for_descendant<StructT, AncestorT>());
	}	  
      } /*adopt_ancestors*/

    private:
      /* set irrevocably to true when .complete() runs.
       *
       * want to reflect a particular type once;
       * short-circuit 2nd or later attempts on the same type
       */
      static bool s_reflected_flag;

      /* type description object for StructT */
      TypeDescrW td_;

      /* members of StructT (at least those we're choosing to reflect) */
      std::vector<StructMember> member_v_;
    }; /*StructReflector*/

    template<typename StructT>
    bool StructReflector<StructT>::s_reflected_flag = false;
  } /*namespace reflect*/

  /* e.g.
   *   struct Foo { int bar_; };
   *   struct Bar : public Foo { .. };
   *
   *   StructReflector<Bar> sr;
   *   REFLECT_EXPLICIT_MEMBER(sr, "bar", &Foo::bar_);
   */
#define REFLECT_EXPLICIT_MEMBER(sr, member_name, member) sr.reflect_member(member_name, member)

  /* e.g.
   *   struct Foo { int bar_; };
   *
   *   StructReflector<Foo> sr;
   *   REFLECT_LITERAL_MEMBER(sr, bar_);
   *
   * then REFLECT_LITERAL_MEMBER() expands to something like:
   *   sr.reflect_member("bar_", &StructReflector<Foo>::struct_t::bar_)
   */
#define REFLECT_LITERAL_MEMBER(sr, member_name) sr.reflect_member(#member_name, &decltype(sr)::struct_t::member_name)

  /* like REFLECT_LITERAL_MEMBER(),  but append trailing underscore
   *
   * minor convenience,  so we can write
   *   struct Foo { int bar_; };
   *
   *   StructReflector<Foo> sr;
   *   REFLECT_MEMBER(sr, bar);   // reflects Foo::bar_ as "bar"
   */
#define REFLECT_MEMBER(sr, member_name) sr.reflect_member(#member_name, &decltype(sr)::struct_t::member_name##_)

} /*namespace xo*/