diff --git a/develop/singles/headers/meta.hpp/meta_all.hpp b/develop/singles/headers/meta.hpp/meta_all.hpp
index c5cddf2..fa00100 100644
--- a/develop/singles/headers/meta.hpp/meta_all.hpp
+++ b/develop/singles/headers/meta.hpp/meta_all.hpp
@@ -441,12 +441,12 @@ namespace meta_hpp::detail
             return *this;
         }
 
-        [[nodiscard]] bool is_empty() const noexcept {
-            return vtable_ == nullptr;
+        [[nodiscard]] bool is_valid() const noexcept {
+            return vtable_ != nullptr;
         }
 
         [[nodiscard]] explicit operator bool() const noexcept {
-            return vtable_ != nullptr;
+            return is_valid();
         }
 
         R operator()(Args... args) const {
@@ -1088,12 +1088,12 @@ namespace meta_hpp::detail
             reset();
         }
 
-        [[nodiscard]] bool is_empty() const noexcept {
-            return data_ == nullptr;
+        [[nodiscard]] bool is_valid() const noexcept {
+            return data_ != nullptr;
         }
 
         [[nodiscard]] explicit operator bool() const noexcept {
-            return data_ != nullptr;
+            return is_valid();
         }
 
         void reset() noexcept {
@@ -2235,12 +2235,12 @@ namespace meta_hpp
         type_base& operator=(type_base&&) noexcept = default;
         type_base& operator=(const type_base&) = default;
 
-        [[nodiscard]] bool is_empty() const noexcept {
-            return data_ == nullptr;
+        [[nodiscard]] bool is_valid() const noexcept {
+            return data_ != nullptr;
         }
 
         [[nodiscard]] explicit operator bool() const noexcept {
-            return data_ != nullptr;
+            return is_valid();
         }
 
         [[nodiscard]] type_id get_id() const noexcept {
@@ -2497,7 +2497,7 @@ namespace std
     template < meta_hpp::detail::type_family Type >
     struct hash<Type> {
         size_t operator()(const Type& type) const noexcept {
-            return type.is_empty() ? 0 : type.get_id().get_hash();
+            return type.is_valid() ? type.get_id().get_hash() : 0;
         }
     };
 }
@@ -2506,15 +2506,15 @@ namespace meta_hpp
 {
     template < detail::type_family L, detail::type_family R >
     [[nodiscard]] bool operator==(const L& l, const R& r) noexcept {
-        return l.is_empty() == r.is_empty() && (l.is_empty() || l.get_id() == r.get_id());
+        return l.is_valid() == r.is_valid() && (!l.is_valid() || l.get_id() == r.get_id());
     }
 
     template < detail::type_family L, detail::type_family R >
     [[nodiscard]] std::strong_ordering operator<=>(const L& l, const R& r) noexcept {
-        if ( const std::strong_ordering cmp{!l.is_empty() <=> !r.is_empty()}; cmp != std::strong_ordering::equal ) {
+        if ( const std::strong_ordering cmp{l.is_valid() <=> r.is_valid()}; cmp != std::strong_ordering::equal ) {
             return cmp;
         }
-        return l.is_empty() ? std::strong_ordering::equal : l.get_id() <=> r.get_id();
+        return l.is_valid() ? l.get_id() <=> r.get_id() : std::strong_ordering::equal;
     }
 }
 
@@ -2522,12 +2522,12 @@ namespace meta_hpp
 {
     template < detail::type_family L >
     [[nodiscard]] bool operator==(const L& l, type_id r) noexcept {
-        return !l.is_empty() && l.get_id() == r;
+        return l.is_valid() && l.get_id() == r;
     }
 
     template < detail::type_family L >
     [[nodiscard]] std::strong_ordering operator<=>(const L& l, type_id r) noexcept {
-        return !l.is_empty() ? l.get_id() <=> r : std::strong_ordering::less;
+        return l.is_valid() ? l.get_id() <=> r : std::strong_ordering::less;
     }
 }
 
@@ -3366,12 +3366,12 @@ namespace meta_hpp
         state_base& operator=(state_base&&) noexcept = default;
         state_base& operator=(const state_base&) = default;
 
-        [[nodiscard]] bool is_empty() const noexcept {
-            return state_ == nullptr;
+        [[nodiscard]] bool is_valid() const noexcept {
+            return state_ != nullptr;
         }
 
         [[nodiscard]] explicit operator bool() const noexcept {
-            return state_ != nullptr;
+            return is_valid();
         }
 
         [[nodiscard]] const index_type& get_index() const noexcept {
@@ -3632,7 +3632,7 @@ namespace std
     template < meta_hpp::detail::state_family State >
     struct hash<State> {
         size_t operator()(const State& state) const noexcept {
-            return state.is_empty() ? 0 : state.get_index().get_hash();
+            return state.is_valid() ? state.get_index().get_hash() : 0;
         }
     };
 }
@@ -3641,15 +3641,15 @@ namespace meta_hpp
 {
     template < detail::state_family L, detail::state_family R >
     [[nodiscard]] bool operator==(const L& l, const R& r) noexcept {
-        return l.is_empty() == r.is_empty() && (l.is_empty() || l.get_index() == r.get_index());
+        return l.is_valid() == r.is_valid() && (!l.is_valid() || l.get_index() == r.get_index());
     }
 
     template < detail::state_family L, detail::state_family R >
     [[nodiscard]] std::strong_ordering operator<=>(const L& l, const R& r) noexcept {
-        if ( const std::strong_ordering cmp{!l.is_empty() <=> !r.is_empty()}; cmp != std::strong_ordering::equal ) {
+        if ( const std::strong_ordering cmp{l.is_valid() <=> r.is_valid()}; cmp != std::strong_ordering::equal ) {
             return cmp;
         }
-        return l.is_empty() ? std::strong_ordering::equal : l.get_index() <=> r.get_index();
+        return l.is_valid() ? l.get_index() <=> r.get_index() : std::strong_ordering::equal;
     }
 }
 
@@ -3657,12 +3657,12 @@ namespace meta_hpp
 {
     template < detail::state_family L, detail::index_family R >
     [[nodiscard]] bool operator==(const L& l, const R& r) noexcept {
-        return !l.is_empty() && l.get_index() == r;
+        return l.is_valid() && l.get_index() == r;
     }
 
     template < detail::state_family L, detail::index_family R >
     [[nodiscard]] std::strong_ordering operator<=>(const L& l, const R& r) noexcept {
-        return !l.is_empty() ? l.get_index() <=> r : std::strong_ordering::less;
+        return l.is_valid() ? l.get_index() <=> r : std::strong_ordering::less;
     }
 }
 
@@ -7873,7 +7873,7 @@ namespace meta_hpp
     }
 
     inline bool class_type::is_base_of(const class_type& derived) const noexcept {
-        if ( is_empty() || derived.is_empty() ) {
+        if ( !is_valid() || !derived.is_valid() ) {
             return false;
         }
 
@@ -7897,7 +7897,7 @@ namespace meta_hpp
     }
 
     inline bool class_type::is_derived_from(const class_type& base) const noexcept {
-        if ( is_empty() || base.is_empty() ) {
+        if ( !is_valid() || !base.is_valid() ) {
             return false;
         }
 
diff --git a/develop/unbench/invoke_function_bench.cpp b/develop/unbench/invoke_function_bench.cpp
index 470c094..2d58ef2 100644
--- a/develop/unbench/invoke_function_bench.cpp
+++ b/develop/unbench/invoke_function_bench.cpp
@@ -128,7 +128,7 @@ namespace
     [[maybe_unused]]
     void meta_invoke_function_1(benchmark::State &state) {
         meta::function f = meta_bench_scope.get_function("static_function_1");
-        META_HPP_ASSERT(!f.is_empty());
+        META_HPP_ASSERT(f.is_valid());
 
         for ( auto _ : state ) {
             f(static_angle);
@@ -138,7 +138,7 @@ namespace
     [[maybe_unused]]
     void meta_invoke_function_2(benchmark::State &state) {
         meta::function f = meta_bench_scope.get_function("static_function_2");
-        META_HPP_ASSERT(!f.is_empty());
+        META_HPP_ASSERT(f.is_valid());
 
         for ( auto _ : state ) {
             f(static_angle, vmath::unit3_x<float>);
@@ -148,7 +148,7 @@ namespace
     [[maybe_unused]]
     void meta_invoke_function_3(benchmark::State &state) {
         meta::function f = meta_bench_scope.get_function("static_function_3");
-        META_HPP_ASSERT(!f.is_empty());
+        META_HPP_ASSERT(f.is_valid());
 
         for ( auto _ : state ) {
             f(static_angle, vmath::unit3_x<float>, 2.f);
@@ -158,7 +158,7 @@ namespace
     [[maybe_unused]]
     void meta_invoke_function_4(benchmark::State &state) {
         meta::function f = meta_bench_scope.get_function("static_function_4");
-        META_HPP_ASSERT(!f.is_empty());
+        META_HPP_ASSERT(f.is_valid());
 
         for ( auto _ : state ) {
             f(static_angle, vmath::unit3_x<float>, 2.f, vmath::midentity3<float>);
diff --git a/develop/untests/meta_base/fixed_function_tests.cpp b/develop/untests/meta_base/fixed_function_tests.cpp
index 8e32ada..ca163b8 100644
--- a/develop/untests/meta_base/fixed_function_tests.cpp
+++ b/develop/untests/meta_base/fixed_function_tests.cpp
@@ -15,12 +15,12 @@ TEST_CASE("meta/meta_base/fixed_function") {
         {
             fixed_function<void()> ff;
             CHECK_FALSE(ff);
-            CHECK(ff.is_empty());
+            CHECK_FALSE(ff.is_valid());
         }
         {
             fixed_function<void()> ff = []{};
             CHECK(ff);
-            CHECK_FALSE(ff.is_empty());
+            CHECK(ff.is_valid());
         }
     }
 
@@ -46,11 +46,11 @@ TEST_CASE("meta/meta_base/fixed_function") {
 
         ff.reset();
         CHECK_FALSE(ff);
-        CHECK(ff.is_empty());
+        CHECK_FALSE(ff.is_valid());
 
         ff = []{return 1;};
         CHECK(ff);
-        CHECK_FALSE(ff.is_empty());
+        CHECK(ff.is_valid());
 
         CHECK(ff() == 1);
     }
diff --git a/develop/untests/meta_base/memory_buffer_tests.cpp b/develop/untests/meta_base/memory_buffer_tests.cpp
index 5413695..5804f6c 100644
--- a/develop/untests/meta_base/memory_buffer_tests.cpp
+++ b/develop/untests/meta_base/memory_buffer_tests.cpp
@@ -15,7 +15,7 @@ TEST_CASE("meta/meta_base/memory_buffer") {
         memory_buffer buf;
 
         CHECK(!buf);
-        CHECK(buf.is_empty());
+        CHECK_FALSE(buf.is_valid());
 
         CHECK(buf.get_size() == 0);
         CHECK(buf.get_align() == std::align_val_t{});
@@ -32,7 +32,7 @@ TEST_CASE("meta/meta_base/memory_buffer") {
 
         {
             CHECK(!buf1);
-            CHECK(buf1.is_empty());
+            CHECK_FALSE(buf1.is_valid());
 
             CHECK(buf1.get_size() == 0);
             CHECK(buf1.get_align() == std::align_val_t{});
@@ -43,7 +43,7 @@ TEST_CASE("meta/meta_base/memory_buffer") {
 
         {
             CHECK(buf2);
-            CHECK(!buf2.is_empty());
+            CHECK(buf2.is_valid());
 
             CHECK(buf2.get_size() == 10);
             CHECK(buf2.get_align() == std::align_val_t{32});
@@ -57,7 +57,7 @@ TEST_CASE("meta/meta_base/memory_buffer") {
         memory_buffer buf{10, std::align_val_t{32}};
 
         CHECK(buf);
-        CHECK(!buf.is_empty());
+        CHECK(buf.is_valid());
 
         CHECK(buf.get_size() == 10);
         CHECK(buf.get_align() == std::align_val_t{32});
@@ -82,7 +82,7 @@ TEST_CASE("meta/meta_base/memory_buffer") {
 
         {
             CHECK(!buf1);
-            CHECK(buf1.is_empty());
+            CHECK_FALSE(buf1.is_valid());
 
             CHECK(buf1.get_size() == 0);
             CHECK(buf1.get_align() == std::align_val_t{});
@@ -93,7 +93,7 @@ TEST_CASE("meta/meta_base/memory_buffer") {
 
         {
             CHECK(buf2);
-            CHECK(!buf2.is_empty());
+            CHECK(buf2.is_valid());
 
             CHECK(buf2.get_size() == 10);
             CHECK(buf2.get_align() == std::align_val_t{32});
@@ -112,7 +112,7 @@ TEST_CASE("meta/meta_base/memory_buffer") {
 
         {
             CHECK(!buf1);
-            CHECK(buf1.is_empty());
+            CHECK_FALSE(buf1.is_valid());
 
             CHECK(buf1.get_size() == 0);
             CHECK(buf1.get_align() == std::align_val_t{});
@@ -123,7 +123,7 @@ TEST_CASE("meta/meta_base/memory_buffer") {
 
         {
             CHECK(buf2);
-            CHECK(!buf2.is_empty());
+            CHECK(buf2.is_valid());
 
             CHECK(buf2.get_size() == 10);
             CHECK(buf2.get_align() == std::align_val_t{32});
@@ -138,7 +138,7 @@ TEST_CASE("meta/meta_base/memory_buffer") {
         buf.reset();
 
         CHECK(!buf);
-        CHECK(buf.is_empty());
+        CHECK_FALSE(buf.is_valid());
 
         CHECK(buf.get_size() == 0);
         CHECK(buf.get_align() == std::align_val_t{});
diff --git a/develop/untests/meta_states/evalue_tests.cpp b/develop/untests/meta_states/evalue_tests.cpp
index 650e50e..a6b5b42 100644
--- a/develop/untests/meta_states/evalue_tests.cpp
+++ b/develop/untests/meta_states/evalue_tests.cpp
@@ -34,7 +34,7 @@ TEST_CASE("meta/meta_states/evalue") {
     SUBCASE("") {
         const meta::evalue evalue;
         CHECK_FALSE(evalue);
-        CHECK(evalue.is_empty());
+        CHECK_FALSE(evalue.is_valid());
         CHECK(evalue == color_type.get_evalue("non-existent-evalue"));
     }
 
diff --git a/develop/untests/meta_states/function_tests.cpp b/develop/untests/meta_states/function_tests.cpp
index 6ae8a98..8fd3a42 100644
--- a/develop/untests/meta_states/function_tests.cpp
+++ b/develop/untests/meta_states/function_tests.cpp
@@ -51,7 +51,7 @@ TEST_CASE("meta/meta_states/function") {
     SUBCASE("") {
         const meta::function func;
         CHECK_FALSE(func);
-        CHECK(func.is_empty());
+        CHECK_FALSE(func.is_valid());
         CHECK(func == ivec2_type.get_function("non-existent-function"));
     }
 
diff --git a/develop/untests/meta_states/member_tests.cpp b/develop/untests/meta_states/member_tests.cpp
index d21e863..2b338ad 100644
--- a/develop/untests/meta_states/member_tests.cpp
+++ b/develop/untests/meta_states/member_tests.cpp
@@ -38,7 +38,7 @@ TEST_CASE("meta/meta_states/member") {
     SUBCASE("") {
         const meta::member member;
         CHECK_FALSE(member);
-        CHECK(member.is_empty());
+        CHECK_FALSE(member.is_valid());
         CHECK(member == clazz_1_type.get_member("non-existent-member"));
     }
 
diff --git a/develop/untests/meta_states/method_tests.cpp b/develop/untests/meta_states/method_tests.cpp
index 39378a1..7896505 100644
--- a/develop/untests/meta_states/method_tests.cpp
+++ b/develop/untests/meta_states/method_tests.cpp
@@ -102,7 +102,7 @@ TEST_CASE("meta/meta_states/method") {
     SUBCASE("") {
         const meta::method method;
         CHECK_FALSE(method);
-        CHECK(method.is_empty());
+        CHECK_FALSE(method.is_valid());
         CHECK(method == ct.get_method("non-existent-method"));
     }
 
diff --git a/develop/untests/meta_states/scope_tests.cpp b/develop/untests/meta_states/scope_tests.cpp
index d1ba989..8be6265 100644
--- a/develop/untests/meta_states/scope_tests.cpp
+++ b/develop/untests/meta_states/scope_tests.cpp
@@ -57,7 +57,7 @@ TEST_CASE("meta/meta_states/scope") {
 
     const meta::scope math_scope = meta::resolve_scope("meta/meta_states/scope/math");
     REQUIRE(math_scope);
-    REQUIRE(!math_scope.is_empty());
+    REQUIRE(math_scope.is_valid());
 
     CHECK(math_scope.get_name() == "meta/meta_states/scope/math");
     CHECK(math_scope.get_variables().size() == 2);
@@ -66,7 +66,7 @@ TEST_CASE("meta/meta_states/scope") {
     SUBCASE("") {
         const meta::scope scope;
         CHECK_FALSE(scope);
-        CHECK(scope.is_empty());
+        CHECK_FALSE(scope.is_valid());
     }
 
     SUBCASE("operators") {
diff --git a/develop/untests/meta_states/variable_tests.cpp b/develop/untests/meta_states/variable_tests.cpp
index 26dffbf..d28e2d1 100644
--- a/develop/untests/meta_states/variable_tests.cpp
+++ b/develop/untests/meta_states/variable_tests.cpp
@@ -68,7 +68,7 @@ TEST_CASE("meta/meta_states/variable") {
     SUBCASE("") {
         const meta::variable variable;
         CHECK_FALSE(variable);
-        CHECK(variable.is_empty());
+        CHECK_FALSE(variable.is_valid());
         CHECK(variable == clazz_1_type.get_variable("non-existent-variable"));
     }
 
diff --git a/develop/untests/meta_types/any_type_tests.cpp b/develop/untests/meta_types/any_type_tests.cpp
index 15cfc32..1f851b0 100644
--- a/develop/untests/meta_types/any_type_tests.cpp
+++ b/develop/untests/meta_types/any_type_tests.cpp
@@ -39,7 +39,7 @@ TEST_CASE("meta/meta_types/any_type") {
     SUBCASE("") {
         const meta::any_type type{};
         CHECK_FALSE(type);
-        CHECK(type.is_empty());
+        CHECK_FALSE(type.is_valid());
 
         CHECK_FALSE(type.is_array());
         CHECK_FALSE(type.as_array());
diff --git a/develop/untests/meta_types/array_type_tests.cpp b/develop/untests/meta_types/array_type_tests.cpp
index eb5f54d..eb46470 100644
--- a/develop/untests/meta_types/array_type_tests.cpp
+++ b/develop/untests/meta_types/array_type_tests.cpp
@@ -13,7 +13,7 @@ TEST_CASE("meta/meta_types/array_type") {
     SUBCASE("") {
         const meta::array_type type;
         CHECK_FALSE(type);
-        CHECK(type.is_empty());
+        CHECK_FALSE(type.is_valid());
     }
 
     SUBCASE("int[]") {
diff --git a/develop/untests/meta_types/function_type_tests.cpp b/develop/untests/meta_types/function_type_tests.cpp
index c4fdbe1..f445018 100644
--- a/develop/untests/meta_types/function_type_tests.cpp
+++ b/develop/untests/meta_types/function_type_tests.cpp
@@ -30,7 +30,7 @@ TEST_CASE("meta/meta_types/function_type") {
     SUBCASE("") {
         const meta::function_type type;
         CHECK_FALSE(type);
-        CHECK(type.is_empty());
+        CHECK_FALSE(type.is_valid());
     }
 
     SUBCASE("arg_copy") {
diff --git a/develop/untests/meta_types/member_type_tests.cpp b/develop/untests/meta_types/member_type_tests.cpp
index 600930d..695ddbd 100644
--- a/develop/untests/meta_types/member_type_tests.cpp
+++ b/develop/untests/meta_types/member_type_tests.cpp
@@ -21,7 +21,7 @@ TEST_CASE("meta/meta_types/member_type") {
     SUBCASE("") {
         const meta::member_type type;
         CHECK_FALSE(type);
-        CHECK(type.is_empty());
+        CHECK_FALSE(type.is_valid());
     }
 
     SUBCASE("int") {
diff --git a/develop/untests/meta_types/method_type_tests.cpp b/develop/untests/meta_types/method_type_tests.cpp
index db14c8a..90b982e 100644
--- a/develop/untests/meta_types/method_type_tests.cpp
+++ b/develop/untests/meta_types/method_type_tests.cpp
@@ -33,7 +33,7 @@ TEST_CASE("meta/meta_types/method_type") {
     SUBCASE("") {
         const meta::method_type type;
         CHECK_FALSE(type);
-        CHECK(type.is_empty());
+        CHECK_FALSE(type.is_valid());
     }
 
     SUBCASE("ivec2::at") {
diff --git a/develop/untests/meta_types/number_type_tests.cpp b/develop/untests/meta_types/number_type_tests.cpp
index a03731c..d9dc437 100644
--- a/develop/untests/meta_types/number_type_tests.cpp
+++ b/develop/untests/meta_types/number_type_tests.cpp
@@ -13,7 +13,7 @@ TEST_CASE("meta/meta_types/number_type") {
     SUBCASE("") {
         const meta::number_type type;
         CHECK_FALSE(type);
-        CHECK(type.is_empty());
+        CHECK_FALSE(type.is_valid());
     }
 
     SUBCASE("int") {
diff --git a/develop/untests/meta_types/pointer_type_tests.cpp b/develop/untests/meta_types/pointer_type_tests.cpp
index 7fbff76..acbeff2 100644
--- a/develop/untests/meta_types/pointer_type_tests.cpp
+++ b/develop/untests/meta_types/pointer_type_tests.cpp
@@ -13,7 +13,7 @@ TEST_CASE("meta/meta_types/pointer_type") {
     SUBCASE("") {
         const meta::pointer_type type;
         CHECK_FALSE(type);
-        CHECK(type.is_empty());
+        CHECK_FALSE(type.is_valid());
     }
 
     SUBCASE("int*") {
diff --git a/develop/untests/meta_types/reference_type_tests.cpp b/develop/untests/meta_types/reference_type_tests.cpp
index f809b01..85b5ceb 100644
--- a/develop/untests/meta_types/reference_type_tests.cpp
+++ b/develop/untests/meta_types/reference_type_tests.cpp
@@ -13,7 +13,7 @@ TEST_CASE("meta/meta_types/reference_type") {
     SUBCASE("") {
         const meta::reference_type type;
         CHECK_FALSE(type);
-        CHECK(type.is_empty());
+        CHECK_FALSE(type.is_valid());
     }
 
     SUBCASE("int&") {
diff --git a/develop/untests/meta_types/void_type_tests.cpp b/develop/untests/meta_types/void_type_tests.cpp
index 855940f..1d89669 100644
--- a/develop/untests/meta_types/void_type_tests.cpp
+++ b/develop/untests/meta_types/void_type_tests.cpp
@@ -13,7 +13,7 @@ TEST_CASE("meta/meta_types/void_type") {
     SUBCASE("") {
         const meta::void_type type;
         CHECK_FALSE(type);
-        CHECK(type.is_empty());
+        CHECK_FALSE(type.is_valid());
     }
 
     SUBCASE("void") {
diff --git a/headers/meta.hpp/meta_base/fixed_function.hpp b/headers/meta.hpp/meta_base/fixed_function.hpp
index a86e7da..a39275f 100644
--- a/headers/meta.hpp/meta_base/fixed_function.hpp
+++ b/headers/meta.hpp/meta_base/fixed_function.hpp
@@ -60,12 +60,12 @@ namespace meta_hpp::detail
             return *this;
         }
 
-        [[nodiscard]] bool is_empty() const noexcept {
-            return vtable_ == nullptr;
+        [[nodiscard]] bool is_valid() const noexcept {
+            return vtable_ != nullptr;
         }
 
         [[nodiscard]] explicit operator bool() const noexcept {
-            return vtable_ != nullptr;
+            return is_valid();
         }
 
         R operator()(Args... args) const {
diff --git a/headers/meta.hpp/meta_base/memory_buffer.hpp b/headers/meta.hpp/meta_base/memory_buffer.hpp
index 0838e59..0c0155e 100644
--- a/headers/meta.hpp/meta_base/memory_buffer.hpp
+++ b/headers/meta.hpp/meta_base/memory_buffer.hpp
@@ -50,12 +50,12 @@ namespace meta_hpp::detail
             reset();
         }
 
-        [[nodiscard]] bool is_empty() const noexcept {
-            return data_ == nullptr;
+        [[nodiscard]] bool is_valid() const noexcept {
+            return data_ != nullptr;
         }
 
         [[nodiscard]] explicit operator bool() const noexcept {
-            return data_ != nullptr;
+            return is_valid();
         }
 
         void reset() noexcept {
diff --git a/headers/meta.hpp/meta_states.hpp b/headers/meta.hpp/meta_states.hpp
index 8ead6a2..a11f35e 100644
--- a/headers/meta.hpp/meta_states.hpp
+++ b/headers/meta.hpp/meta_states.hpp
@@ -133,12 +133,12 @@ namespace meta_hpp
         state_base& operator=(state_base&&) noexcept = default;
         state_base& operator=(const state_base&) = default;
 
-        [[nodiscard]] bool is_empty() const noexcept {
-            return state_ == nullptr;
+        [[nodiscard]] bool is_valid() const noexcept {
+            return state_ != nullptr;
         }
 
         [[nodiscard]] explicit operator bool() const noexcept {
-            return state_ != nullptr;
+            return is_valid();
         }
 
         [[nodiscard]] const index_type& get_index() const noexcept {
@@ -399,7 +399,7 @@ namespace std
     template < meta_hpp::detail::state_family State >
     struct hash<State> {
         size_t operator()(const State& state) const noexcept {
-            return state.is_empty() ? 0 : state.get_index().get_hash();
+            return state.is_valid() ? state.get_index().get_hash() : 0;
         }
     };
 }
@@ -408,15 +408,15 @@ namespace meta_hpp
 {
     template < detail::state_family L, detail::state_family R >
     [[nodiscard]] bool operator==(const L& l, const R& r) noexcept {
-        return l.is_empty() == r.is_empty() && (l.is_empty() || l.get_index() == r.get_index());
+        return l.is_valid() == r.is_valid() && (!l.is_valid() || l.get_index() == r.get_index());
     }
 
     template < detail::state_family L, detail::state_family R >
     [[nodiscard]] std::strong_ordering operator<=>(const L& l, const R& r) noexcept {
-        if ( const std::strong_ordering cmp{!l.is_empty() <=> !r.is_empty()}; cmp != std::strong_ordering::equal ) {
+        if ( const std::strong_ordering cmp{l.is_valid() <=> r.is_valid()}; cmp != std::strong_ordering::equal ) {
             return cmp;
         }
-        return l.is_empty() ? std::strong_ordering::equal : l.get_index() <=> r.get_index();
+        return l.is_valid() ? l.get_index() <=> r.get_index() : std::strong_ordering::equal;
     }
 }
 
@@ -424,12 +424,12 @@ namespace meta_hpp
 {
     template < detail::state_family L, detail::index_family R >
     [[nodiscard]] bool operator==(const L& l, const R& r) noexcept {
-        return !l.is_empty() && l.get_index() == r;
+        return l.is_valid() && l.get_index() == r;
     }
 
     template < detail::state_family L, detail::index_family R >
     [[nodiscard]] std::strong_ordering operator<=>(const L& l, const R& r) noexcept {
-        return !l.is_empty() ? l.get_index() <=> r : std::strong_ordering::less;
+        return l.is_valid() ? l.get_index() <=> r : std::strong_ordering::less;
     }
 }
 
diff --git a/headers/meta.hpp/meta_types.hpp b/headers/meta.hpp/meta_types.hpp
index 37ec974..dad913c 100644
--- a/headers/meta.hpp/meta_types.hpp
+++ b/headers/meta.hpp/meta_types.hpp
@@ -65,12 +65,12 @@ namespace meta_hpp
         type_base& operator=(type_base&&) noexcept = default;
         type_base& operator=(const type_base&) = default;
 
-        [[nodiscard]] bool is_empty() const noexcept {
-            return data_ == nullptr;
+        [[nodiscard]] bool is_valid() const noexcept {
+            return data_ != nullptr;
         }
 
         [[nodiscard]] explicit operator bool() const noexcept {
-            return data_ != nullptr;
+            return is_valid();
         }
 
         [[nodiscard]] type_id get_id() const noexcept {
@@ -327,7 +327,7 @@ namespace std
     template < meta_hpp::detail::type_family Type >
     struct hash<Type> {
         size_t operator()(const Type& type) const noexcept {
-            return type.is_empty() ? 0 : type.get_id().get_hash();
+            return type.is_valid() ? type.get_id().get_hash() : 0;
         }
     };
 }
@@ -336,15 +336,15 @@ namespace meta_hpp
 {
     template < detail::type_family L, detail::type_family R >
     [[nodiscard]] bool operator==(const L& l, const R& r) noexcept {
-        return l.is_empty() == r.is_empty() && (l.is_empty() || l.get_id() == r.get_id());
+        return l.is_valid() == r.is_valid() && (!l.is_valid() || l.get_id() == r.get_id());
     }
 
     template < detail::type_family L, detail::type_family R >
     [[nodiscard]] std::strong_ordering operator<=>(const L& l, const R& r) noexcept {
-        if ( const std::strong_ordering cmp{!l.is_empty() <=> !r.is_empty()}; cmp != std::strong_ordering::equal ) {
+        if ( const std::strong_ordering cmp{l.is_valid() <=> r.is_valid()}; cmp != std::strong_ordering::equal ) {
             return cmp;
         }
-        return l.is_empty() ? std::strong_ordering::equal : l.get_id() <=> r.get_id();
+        return l.is_valid() ? l.get_id() <=> r.get_id() : std::strong_ordering::equal;
     }
 }
 
@@ -352,12 +352,12 @@ namespace meta_hpp
 {
     template < detail::type_family L >
     [[nodiscard]] bool operator==(const L& l, type_id r) noexcept {
-        return !l.is_empty() && l.get_id() == r;
+        return l.is_valid() && l.get_id() == r;
     }
 
     template < detail::type_family L >
     [[nodiscard]] std::strong_ordering operator<=>(const L& l, type_id r) noexcept {
-        return !l.is_empty() ? l.get_id() <=> r : std::strong_ordering::less;
+        return l.is_valid() ? l.get_id() <=> r : std::strong_ordering::less;
     }
 }
 
diff --git a/headers/meta.hpp/meta_types/class_type.hpp b/headers/meta.hpp/meta_types/class_type.hpp
index 67a7c83..25bb524 100644
--- a/headers/meta.hpp/meta_types/class_type.hpp
+++ b/headers/meta.hpp/meta_types/class_type.hpp
@@ -135,7 +135,7 @@ namespace meta_hpp
     }
 
     inline bool class_type::is_base_of(const class_type& derived) const noexcept {
-        if ( is_empty() || derived.is_empty() ) {
+        if ( !is_valid() || !derived.is_valid() ) {
             return false;
         }
 
@@ -159,7 +159,7 @@ namespace meta_hpp
     }
 
     inline bool class_type::is_derived_from(const class_type& base) const noexcept {
-        if ( is_empty() || base.is_empty() ) {
+        if ( !is_valid() || !base.is_valid() ) {
             return false;
         }