From 8c462b83a159d6408cde1b1817cf452d34041806 Mon Sep 17 00:00:00 2001
From: Stephen Seo <seo.disparate@gmail.com>
Date: Tue, 11 Sep 2018 12:16:04 +0900
Subject: [PATCH] Add static_assert, components must be def-const

EC::Manager will fail to compile if any given Component is not default
constructible, so a static_assert and ctest was added.
---
 .gitignore                       |  3 ++-
 src/CMakeLists.txt               | 11 +++++++++++
 src/EC/Manager.hpp               |  6 ++++++
 src/test/WillFailCompileTest.cpp | 24 ++++++++++++++++++++++++
 4 files changed, 43 insertions(+), 1 deletion(-)
 create mode 100644 src/test/WillFailCompileTest.cpp

diff --git a/.gitignore b/.gitignore
index e76c31b..ae041a3 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,4 +2,5 @@ build*/
 *.o
 *.swp
 doxygen_html/
-
+compile_commands.json
+tags
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 56e7b47..0244e2b 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -16,6 +16,9 @@ set(EntityComponentSystem_HEADERS
     EC/Manager.hpp
     EC/EC.hpp)
 
+set(WillFailCompile_SOURCES
+    test/WillFailCompileTest.cpp)
+
 add_library(EntityComponentSystem INTERFACE)
 target_link_libraries(EntityComponentSystem INTERFACE pthread)
 target_include_directories(EntityComponentSystem INTERFACE ${CMAKE_CURRENT_SOURCE_DIR})
@@ -56,3 +59,11 @@ if(GTEST_FOUND)
     add_test(NAME UnitTests COMMAND UnitTests)
 endif()
 
+add_executable(WillFailCompile ${WillFailCompile_SOURCES})
+set_target_properties(WillFailCompile PROPERTIES
+    EXCLUDE_FROM_ALL True
+    EXCLUDE_FROM_DEFAULT_BUILD True)
+add_test(NAME WillFailCompile_0
+    COMMAND ${CMAKE_COMMAND} --build . --target WillFailCompile --config $<CONFIGURATION>
+    WORKING_DIRECTORY ${CMAKE_BINARY_DIR})
+set_tests_properties(WillFailCompile_0 PROPERTIES WILL_FAIL True)
diff --git a/src/EC/Manager.hpp b/src/EC/Manager.hpp
index c8b8a71..4191ce9 100644
--- a/src/EC/Manager.hpp
+++ b/src/EC/Manager.hpp
@@ -22,6 +22,7 @@
 #include <algorithm>
 #include <thread>
 #include <mutex>
+#include <type_traits>
 
 #ifndef NDEBUG
   #include <iostream>
@@ -59,6 +60,10 @@ namespace EC
         using BitsetType = EC::Bitset<ComponentsList, TagsList>;
 
     private:
+        using ComponentsTuple = EC::Meta::Morph<ComponentsList, std::tuple<> >;
+        static_assert(std::is_default_constructible<ComponentsTuple>::value,
+            "All components must be default constructible");
+
         template <typename... Types>
         struct Storage
         {
@@ -66,6 +71,7 @@ namespace EC
         };
         using ComponentsStorage =
             typename EC::Meta::Morph<ComponentsList, Storage<> >::type;
+
         // Entity: isAlive, ComponentsTags Info
         using EntitiesTupleType = std::tuple<bool, BitsetType>;
         using EntitiesType = std::vector<EntitiesTupleType>;
diff --git a/src/test/WillFailCompileTest.cpp b/src/test/WillFailCompileTest.cpp
new file mode 100644
index 0000000..ca62ad3
--- /dev/null
+++ b/src/test/WillFailCompileTest.cpp
@@ -0,0 +1,24 @@
+#include <EC/Manager.hpp>
+
+struct NoDef
+{
+    NoDef(int a) : a(a) {}
+
+    int a;
+};
+
+struct WithDef
+{
+    WithDef() : a(0) {}
+
+    int a;
+};
+
+using EC::Meta::TypeList;
+
+int main()
+{
+    // should fail to compile because "NoDef" is not default constructible
+    EC::Manager<TypeList<WithDef, NoDef>, TypeList<>> manager;
+    return 0;
+}