non constructing allocator

inc/mkn/gpu/alloc.hpp

@@ -31,9 +31,9 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #ifndef _MKN_GPU_ALLOC_HPP_
 #define _MKN_GPU_ALLOC_HPP_
 
-template <typename T, std::int32_t alignment = 32>
-class ManagedAllocator {
-  using This = ManagedAllocator<T, alignment>;
+template <typename T, std::int32_t alignment>
+class MknGPUAllocator {
+  using This = MknGPUAllocator<T, alignment>;
 
  public:
   using pointer = T*;
@@ -42,11 +42,6 @@ class ManagedAllocator {
   using size_type = std::size_t;
   using difference_type = std::ptrdiff_t;
 
-  template <typename U>
-  struct rebind {
-    using other = ManagedAllocator<U, alignment>;
-  };
-
   T* allocate(std::size_t const n) const {
     if (n == 0) return nullptr;
 
@@ -70,6 +65,29 @@ class ManagedAllocator {
   }
 };
 
+template <typename T, std::int32_t alignment = 32>
+class NoConstructAllocator : public MknGPUAllocator<T, alignment> {
+ public:
+  template <typename U>
+  struct rebind {
+    using other = NoConstructAllocator<U, alignment>;
+  };
+
+  template <typename U, typename... Args>
+  void construct(U* /*ptr*/, Args&&... /*args*/) {}  // nothing
+  template <typename U>
+  void construct(U* /*ptr*/) noexcept(std::is_nothrow_default_constructible<U>::value) {}
+};
+
+template <typename T, std::int32_t alignment = 32>
+class ManagedAllocator : public MknGPUAllocator<T, alignment> {
+ public:
+  template <typename U>
+  struct rebind {
+    using other = ManagedAllocator<U, alignment>;
+  };
+};
+
 template <typename T, typename Size>
 void copy(T* const dst, T const* const src, Size size) {
   assert(dst and src);

test/any/construct.cpp

@@ -0,0 +1,35 @@
+
+#include "mkn/gpu.hpp"
+
+static constexpr uint32_t NUM = 10;
+
+template <typename T>
+using ManagedVector = std::vector<T, mkn::gpu::ManagedAllocator<T>>;
+
+template <typename T>
+using ManagedMemory = std::vector<T, mkn::gpu::NoConstructAllocator<T>>;
+
+std::size_t alloced = 0;
+struct S {
+  S() { ++alloced; }
+};
+
+std::uint32_t test_does_construct_on_resize() {
+  alloced = 0;
+  ManagedVector<S> mem{NUM};
+  mem.resize(NUM + NUM);
+  return alloced != NUM + NUM;
+}
+
+std::uint32_t test_does_not_construct_on_resize() {
+  alloced = 0;
+  ManagedMemory<S> mem{NUM};
+  mem.resize(NUM + NUM);
+  return alloced != 0;
+}
+
+int main() {
+  KOUT(NON) << __FILE__;
+
+  return test_does_construct_on_resize() + test_does_not_construct_on_resize();
+}