non-constructing vector

inc/mkn/kul/alloc.hpp

@@ -35,6 +35,7 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #include <cstdint>
 #include <cstddef>
 #include <cstdlib>
+#include <type_traits>
 
 namespace mkn::kul {
 
@@ -81,6 +82,55 @@ class AlignedAllocator {
   }
 };
 
+template <typename T>
+class Allocator {
+  using This = Allocator<T>;
+
+ public:
+  using pointer = T*;
+  using reference = T&;
+  using value_type = T;
+  using size_type = std::size_t;
+  using difference_type = std::ptrdiff_t;
+
+  template <typename U>
+  struct rebind {
+    using other = Allocator<U>;
+  };
+
+  T* allocate(std::size_t const n) const {
+    if (n == 0) return nullptr;
+    void* p = ::operator new(n * sizeof(T));
+    if (!p) throw std::bad_alloc();
+    return static_cast<T*>(p);
+  }
+
+  void deallocate(T* const p) noexcept {
+    if (p) ::operator delete(p);
+  }
+  void deallocate(T* const p, std::size_t /*n*/) noexcept {  // needed from std::
+    if (p) ::operator delete(p);
+  }
+  bool operator!=(This const& that) const { return !(*this == that); }
+  bool operator==(This const& /*that*/) const {
+    return true;  // stateless
+  }
+};
+
+template <typename T>
+class NonConstructingAllocator : public Allocator<T> {
+ public:
+  template <typename U>
+  struct rebind {
+    using other = NonConstructingAllocator<U>;
+  };
+
+  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) {}
+};
+
 }  // namespace mkn::kul
 
 #endif /*_MKN_KUL_ALLOC_HPP_*/

inc/mkn/kul/vector.hpp

@@ -0,0 +1,63 @@
+/**
+Copyright (c) 2022, Philip Deegan.
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+    * Redistributions of source code must retain the above copyright
+notice, this list of conditions and the following disclaimer.
+    * Redistributions in binary form must reproduce the above
+copyright notice, this list of conditions and the following disclaimer
+in the documentation and/or other materials provided with the
+distribution.
+    * Neither the name of Philip Deegan nor the names of its
+contributors may be used to endorse or promote products derived from
+this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+*/
+#ifndef _MKN_KUL_VECTOR_HPP_
+#define _MKN_KUL_VECTOR_HPP_
+
+#include "mkn/kul/alloc.hpp"
+
+#include <vector>
+
+namespace mkn::kul {
+
+template <typename T, typename A = void>  // A ignored but there for std::vector interop
+using NonConstructingVector = std::vector<T, NonConstructingAllocator<T>>;
+
+template <typename T>
+std::vector<T, Allocator<T>>& as_super(std::vector<T, NonConstructingAllocator<T>>& v) {
+  return *reinterpret_cast<std::vector<T, Allocator<T>>*>(&v);
+}
+
+}  // namespace mkn::kul
+
+template <typename T, typename A0, typename A1 = void>
+bool operator==(std::vector<T, A0> const& v0, mkn::kul::NonConstructingVector<T, A1> const& v1) {
+  if (v0.size() != v1.size()) return false;
+  for (std::size_t i = 0; i < v0.size(); i++)
+    if (v0[i] != v1[i]) return false;
+  return true;
+}
+
+template <typename T, typename A0, typename A1 = void>
+bool operator==(mkn::kul::NonConstructingVector<T, A1> const& v0, std::vector<T, A0> const& v1) {
+  return v1 == v0;
+}
+
+#endif /*_MKN_KUL_VECTOR_HPP_*/

test/test/no_construct_alloc.cpp

@@ -0,0 +1,85 @@
+
+
+#include "test_common.hpp"
+
+#include "mkn/kul/dbg.hpp"
+#include "mkn/kul/alloc.hpp"
+#include "mkn/kul/vector.hpp"
+
+#include <array>
+#include <cstddef>
+#include <stdexcept>
+
+template <std::uint8_t size = 8>
+struct S {
+  S() {
+    for (std::uint8_t i = 0; i < size; i++) vars[i] = i;
+  }
+
+  bool operator==(S const& that) const {
+    for (std::size_t i = 0; i < size; i++)
+      if (vars[i] != that.vars[i]) return false;
+
+    return true;
+  }
+
+  std::array<std::size_t, size> vars;
+};
+
+template <typename V>
+auto copy_construct(V const& v) {
+  KUL_DBG_FUNC_ENTER;
+  V out{v};
+  return out;
+}
+
+template <typename V>
+auto copy_operator_equal(V const& v) {
+  KUL_DBG_FUNC_ENTER;
+  V out;
+  out.reserve(v.capacity());
+  out = v;
+  return out;
+}
+
+template <typename V>
+auto copy_manual(V const& v) {
+  KUL_DBG_FUNC_ENTER;
+  V out;
+  out.reserve(v.capacity());
+  out.resize(v.size());
+  std::copy(v.begin(), v.end(), out.begin());
+  return out;
+}
+
+template <typename V>
+auto make_vector(std::size_t const& size) {
+  KUL_DBG_FUNC_ENTER;
+  return V{size};
+}
+template <typename V0, typename V1>
+auto make_vector_from(V1 const& v1) {
+  KUL_DBG_FUNC_ENTER;
+  V0 v(v1.size());
+  std::copy(v1.begin(), v1.end(), v.begin());
+  return v;
+}
+
+template <typename T>
+void do_compare() {
+  constexpr static std::size_t N = 2e6;
+  auto const std_vec = make_vector<std::vector<T>>(N);
+  auto const no_construct_vec = make_vector_from<mkn::kul::NonConstructingVector<T>>(std_vec);
+  if (std_vec != no_construct_vec) throw std::runtime_error("FAIL");
+  auto const v0 = copy_construct(std_vec);
+  auto const v1 = copy_construct(no_construct_vec);
+  auto const v2 = copy_manual(std_vec);
+  auto const v3 = copy_manual(no_construct_vec);
+
+  if (v0 != std_vec) throw std::runtime_error("FAIL 0");
+  if (v0 == v1) throw std::runtime_error("FAIL 1");  // :(
+  if (v0 != v2) throw std::runtime_error("FAIL 2");
+  if (v0 != v3) throw std::runtime_error("FAIL 3");
+}
+
+TEST(NoConstructAllocator, copies) { do_compare<S<8>>(); }