add rtree (#200)

include/cista/cista_member_offset.h

@@ -0,0 +1,33 @@
+#pragma once
+
+#include "cista/offset_t.h"
+
+namespace cista {
+
+template <typename T, typename Member>
+cista::offset_t member_offset(T const* t, Member const* m) {
+  static_assert(std::is_trivially_copyable_v<T>);
+  return (reinterpret_cast<std::uint8_t const*>(m) -
+          reinterpret_cast<std::uint8_t const*>(t));
+}
+
+template <typename T, typename Member>
+offset_t member_offset(T const* t, Member T::*m) {
+  static_assert(std::is_trivially_copyable_v<T>);
+  return (reinterpret_cast<std::uint8_t const*>(&(t->*m)) -
+          reinterpret_cast<std::uint8_t const*>(t));
+}
+
+}  // namespace cista
+
+#ifndef cista_member_offset
+#define cista_member_offset(Type, Member)                            \
+  ([]() {                                                            \
+    if constexpr (std::is_standard_layout_v<Type>) {                 \
+      return static_cast<::cista::offset_t>(offsetof(Type, Member)); \
+    } else {                                                         \
+      return ::cista::member_offset(static_cast<Type*>(nullptr),     \
+                                    &Type::Member);                  \
+    }                                                                \
+  }())
+#endif

include/cista/containers.h

@@ -9,6 +9,7 @@
 #include "cista/containers/mutable_fws_multimap.h"
 #include "cista/containers/nvec.h"
 #include "cista/containers/optional.h"
+#include "cista/containers/rtree.h"
 #include "cista/containers/string.h"
 #include "cista/containers/tuple.h"
 #include "cista/containers/unique_ptr.h"