From 0533360642ff320a1a7d25ed2911a6c44de8d6e9 Mon Sep 17 00:00:00 2001
From: Stanislaw Halik <sthalik@misaki.pl>
Date: Sat, 19 Nov 2022 07:27:49 +0100
Subject: entity: add field enablement predicate

---
 entity/metadata.hpp |  4 ++--
 test/entity.cpp     | 17 +++++++++++++++++
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/entity/metadata.hpp b/entity/metadata.hpp
index a35e0cc6..dc7d9f1d 100644
--- a/entity/metadata.hpp
+++ b/entity/metadata.hpp
@@ -211,10 +211,10 @@ constexpr erased_accessor entity_field<Obj, Type, R, W, P>::erased() const
 
     return erased_accessor {
         (void*)&reader, writer ? (void*)&writer : nullptr,
-        std::is_same_v<P, std::nullptr_t> ? (const void*)&predicate : nullptr,
+        !std::is_same_v<P, std::nullptr_t> ? (const void*)&predicate : nullptr,
         name, obj_name, field_name,
         reader_fn, writer ? writer_fn : writer_stub_fn,
-        std::is_same_v<P, std::nullptr_t> ? predicate_fn : predicate_stub_fn,
+        !std::is_same_v<P, std::nullptr_t> ? predicate_fn : predicate_stub_fn,
     };
 }
 
diff --git a/test/entity.cpp b/test/entity.cpp
index 858c5a11..5db83974 100644
--- a/test/entity.cpp
+++ b/test/entity.cpp
@@ -155,6 +155,22 @@ constexpr bool test_null_writer()
     return true;
 }
 
+void test_predicate()
+{
+    constexpr TestAccessors x{0, 0, 0};
+    constexpr auto m_foo = entity::type<int>::field{"foo"_s, &TestAccessors::foo, &TestAccessors::foo,
+                                                    [](const TestAccessors&) { return false; }};
+    static_assert(!m_foo.is_enabled(m_foo.predicate, x));
+    fm_assert(!m_foo.erased().is_enabled(x));
+    constexpr auto m_foo2 = entity::type<int>::field{"foo"_s, &TestAccessors::foo, &TestAccessors::foo,
+                                                     [](const TestAccessors&) { return true; }};
+    static_assert(m_foo2.is_enabled(m_foo2.predicate, x));
+    fm_assert(m_foo2.erased().is_enabled(x));
+    constexpr auto m_foo3 = entity::type<int>::field{"foo"_s, &TestAccessors::foo, &TestAccessors::foo};
+    static_assert(m_foo3.is_enabled(m_foo3.predicate, x));
+    fm_assert(m_foo3.erased().is_enabled(x));
+}
+
 } // namespace
 
 static constexpr bool test_names()
@@ -179,6 +195,7 @@ void test_app::test_entity()
     static_assert(test_visitor());
     static_assert(test_null_writer());
     static_assert(test_names());
+    test_predicate();
     test_fun2();
     test_erasure();
     test_type_name();
-- 
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