add: [imp] dataof

include/libimp/dataof.h

@@ -0,0 +1,92 @@
+/**
+ * \file libimp/dataof.h
+ * \author mutouyun (orz@orzz.org)
+ * \brief Returns the data pointer of the given range
+ * \date 2023-05-27
+ */
+#pragma once
+
+#include <type_traits>  // std::declval, std::true_type, std::false_type
+#include <cstddef>      // std::size_t
+
+#include "libimp/def.h"
+#include "libimp/generic.h"
+
+LIBIMP_NAMESPACE_BEG_
+
+/**
+ * \see https://en.cppreference.com/w/cpp/iterator/data
+*/
+
+namespace detail_dataof {
+
+template <typename T>
+struct trait_has_data {
+private:
+  template <typename Type>
+  static std::true_type check(decltype(std::declval<Type>().data())*);
+  template <typename Type>
+  static std::false_type check(...);
+public:
+  using type = decltype(check<T>(nullptr));
+  constexpr static auto value = type::value;
+};
+
+template <typename T>
+struct trait_has_Data {
+private:
+  template <typename Type>
+  static std::true_type check(decltype(std::declval<Type>().Data())*);
+  template <typename Type>
+  static std::false_type check(...);
+public:
+  using type = decltype(check<T>(nullptr));
+  constexpr static auto value = type::value;
+};
+
+template <typename C, bool = trait_has_data<C>::value
+                    , bool = trait_has_Data<C>::value>
+struct trait;
+
+template <typename T, std::size_t N>
+struct trait<T[N], false, false> {
+  constexpr static T const *dataof(T const (&arr)[N]) noexcept {
+    return arr;
+  }
+  constexpr static T *dataof(T (&arr)[N]) noexcept {
+    return arr;
+  }
+};
+
+template <typename C, bool B>
+struct trait<C, true, B> {
+  template <typename T>
+  constexpr static auto dataof(T &&c) noexcept(noexcept(c.data())) {
+    return std::forward<T>(c).data();
+  }
+};
+
+template <typename C>
+struct trait<C, false, true> {
+  template <typename T>
+  constexpr static auto dataof(T &&c) noexcept(noexcept(c.Data())) {
+    return std::forward<T>(c).Data();
+  }
+};
+
+template <typename C>
+struct trait<C, false, false> {
+  template <typename T>
+  constexpr static T const *dataof(std::initializer_list<T> il) noexcept {
+    return il.begin();
+  }
+};
+
+} // namespace detail_dataof
+
+template <typename T, typename R = detail_dataof::trait<std::remove_cv_t<std::remove_reference_t<T>>>>
+constexpr auto dataof(T &&c) noexcept(noexcept(R::dataof(std::forward<T>(c)))) {
+  return R::dataof(std::forward<T>(c));
+}
+
+LIBIMP_NAMESPACE_END_

test/imp/test_imp_utility.cpp

@@ -8,6 +8,7 @@
 #include "libimp/construct.h"
 #include "libimp/pimpl.h"
 #include "libimp/countof.h"
+#include "libimp/dataof.h"
 #include "libimp/horrible_cast.h"
 #include "libimp/detect_plat.h"
 #include "libimp/generic.h"
@@ -100,9 +101,27 @@ TEST(utility, countof) {
 
   std::vector<int> vec {1, 2, 3, 4, 5};
   int arr[] {7, 6, 5, 4, 3, 2, 1};
+  auto il = {9, 7, 6, 4, 3, 1, 5};
   EXPECT_EQ(imp::countof(sv) , sv.Size());
   EXPECT_EQ(imp::countof(vec), vec.size());
   EXPECT_EQ(imp::countof(arr), sizeof(arr) / sizeof(arr[0]));
+  EXPECT_EQ(imp::countof(il) , il.size());
+}
+
+TEST(utility, dataof) {
+  struct {
+    constexpr int *Data() const noexcept { return (int *)this; }
+  } sv;
+  EXPECT_FALSE(imp::detail_dataof::trait_has_data<decltype(sv)>::value);
+  EXPECT_TRUE (imp::detail_dataof::trait_has_Data<decltype(sv)>::value);
+
+  std::vector<int> vec {1, 2, 3, 4, 5};
+  int arr[] {7, 6, 5, 4, 3, 2, 1};
+  auto il = {9, 7, 6, 4, 3, 1, 5};
+  EXPECT_EQ(imp::dataof(sv) , sv.Data());
+  EXPECT_EQ(imp::dataof(vec), vec.data());
+  EXPECT_EQ(imp::dataof(arr), arr);
+  EXPECT_EQ(imp::dataof(il) , il.begin());
 }
 
 TEST(utility, horrible_cast) {