Make sizeof test to runtime, query the C++ compiler

We should strive to query the C++ compiler as much as possible
instead of relying on hardcoded values, as it ensures that
any change (new standard, new compiler, new platform) will
catch the bug, which relying on hardcoded value will not.

extras/test.cpp

@@ -10,5 +10,15 @@
 #include <list>
 #include <vector>
 
+namespace stdcpp::test {
+    template<typename T>
+    std::size_t cppSizeOf() {
+        return sizeof(T);
+    }
+};
+
 template class std::list<int>;
+template std::size_t stdcpp::test::cppSizeOf<std::list<int> >();
+
 template class std::vector<int>;
+template std::size_t stdcpp::test::cppSizeOf<std::vector<int> >();

source/stdcpp/test/base.d

@@ -0,0 +1,12 @@
+/*******************************************************************************
+
+    Utilities to be used in tests
+
+*******************************************************************************/
+
+module stdcpp.test.base;
+
+version (unittest):
+
+/// Returns: the `sizeof` of `T` as seen by the C++ compiler
+extern(C++, "stdcpp", "test") size_t cppSizeOf (T) ();

source/stdcpp/test/list.d

@@ -6,15 +6,17 @@
 
 module stdcpp.test.list;
 
+import stdcpp.test.base;
 import stdcpp.list;
 
+/// Test that the sizes matches
 unittest
 {
-    version (CppRuntime_Microsoft)
-        static assert(list!int.sizeof == 16);
-    else
-        static assert(list!int.sizeof == 24);
+    assert(cppSizeOf!(list!int) == list!int.sizeof);
+}
 
+unittest
+{
     auto p = list!int(5);
     p.push_back(5);
     assert(p.size() == 6);

source/stdcpp/test/vector.d

@@ -6,7 +6,15 @@
 
 module stdcpp.test.vector;
 
+import stdcpp.test.base;
 import stdcpp.vector;
+
+/// Test that the sizes matches
+unittest
+{
+    assert(cppSizeOf!(vector!int) == vector!int.sizeof);
+}
+
 version (CppRuntime_Gcc)
 {
     unittest
@@ -39,7 +47,6 @@ version (CppRuntime_Gcc)
         assert(p.capacity() == 12);
         p.resize(5);
         assert(p.length == 5);
-        assert(p.sizeof == 24);//verifying three pointers
         p.assign(3,8);
         assert(p.length == 3);
         p.push_back(4);
@@ -82,7 +89,6 @@ else version (CppRuntime_Clang)
         assert(vec.empty == 0);
         vec.reserve(6);
         assert(vec.capacity == 6);
-        assert(vec.sizeof == 24);
         vec.assign(3,8);
         assert(vec.length == 3);
         assert(vec[0] == 8);
@@ -98,8 +104,5 @@ else version (CppRuntime_Clang)
         vec3.swap(vec);
         assert(vec3.size == 9); // after swap
         assert(vec.size == 7);
-
-
-
     }
 }