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1 /*++
2
3 Copyright (c) Microsoft. All rights reserved.
4
5 Module Name:
6
7 EnumVariantMap.h
8
9 Abstract:
10
11 Template for enum-based variant maps.
12
13 --*/
14 #pragma once
15 #include <map>
16 #include <type_traits>
17 #include <utility>
18 #include <variant>
19 #include <vector>
20
21 // This template set is used for Arg storage and Context Data storage by enum type.
22 // The backing storage is a std::multimap of the enum to a variant of types.
23 // This enables strongly typed storage and retrieval of values based on an enum key.
24 namespace wsl::windows::wslc {
25
26 // Enum based variant helper.
27 // Enum must be an enum whose first member has the value 0, each subsequent member increases by 1, and the final member is named Max.
28 // Mapping is a template type that takes one template parameter of type Enum, and whose members define value_t as the type for that enum value.
29 template <typename Enum, template <Enum> typename Mapping>
30 struct EnumBasedVariant
31 {
32 private:
33 // Used to deduce the variant type; making a variant that includes std::monostate and all Mapping types.
34 template <size_t... I>
35 static inline auto Deduce(std::index_sequence<I...>)
36 {
37 return std::variant<std::monostate, typename Mapping<static_cast<Enum>(I)>::value_t...>{};
38 }
39
40 public:
41 // Holds data of any type listed in Mapping.
42 using variant_t = decltype(Deduce(std::make_index_sequence<static_cast<size_t>(Enum::Max)>()));
43
44 // Gets the index into the variant for the given Data.
45 static constexpr inline size_t Index(Enum e)
46 {
47 return static_cast<size_t>(e) + 1;
48 }
49 };
50
51 // An action that can be taken on an EnumBasedVariantMap.
52 enum class EnumBasedVariantMapAction
53 {
54 Add,
55 Contains,
56 Get,
57 GetMutable,
58 GetAll,
59 Count,
60 Remove,
61 };
62
63 // A callback function that can take any action in response to map operations, such as logging
64 // accesses or maintaining state derived from the map contents.
65 template <typename Enum>
66 using EnumBasedVariantMapActionCallback = void (*)(const void* map, Enum value, EnumBasedVariantMapAction action);
67
68 // Forward declaration for EnumBasedVariantMapEmplacer
69 template <typename Enum, template <Enum> typename Mapping, typename V>
70 struct EnumBasedVariantMapEmplacer;
71
72 // Provides a multimap of the Enum to the mapped types (allows multiple values per key).
73 template <typename Enum, template <Enum> typename Mapping, EnumBasedVariantMapActionCallback<Enum> Callback = nullptr>
74 struct EnumBasedVariantMap
75 {
76 using Variant = EnumBasedVariant<Enum, Mapping>;
77
78 template <Enum E>
79 using mapping_t = typename Mapping<E>::value_t;
80
81 // Adds a value to the map. With multimap, this always adds a new entry (doesn't overwrite).
82 template <Enum E>
83 void Add(mapping_t<E>&& v)
84 {
85 if constexpr (Callback)
86 {
87 Callback(this, E, EnumBasedVariantMapAction::Add);
88 }
89
90 // Compile-time type checking - this should always pass since mapping_t<E> is the correct type
91 using CleanV = std::remove_cvref_t<mapping_t<E>>;
92 static_assert(
93 std::is_same_v<CleanV, mapping_t<E>>,
94 "Type mismatch in Add: provided type does not match the expected type for this enum value");
95
96 typename Variant::variant_t variant;
97 variant.template emplace<Variant::Index(E)>(std::move(v));
98 m_data.emplace(E, std::move(variant));
99 }
100
101 template <Enum E>
102 void Add(const mapping_t<E>& v)
103 {
104 if constexpr (Callback)
105 {
106 Callback(this, E, EnumBasedVariantMapAction::Add);
107 }
108
109 // Compile-time type checking - this should always pass since mapping_t<E> is the correct type
110 using CleanV = std::remove_cvref_t<mapping_t<E>>;
111 static_assert(
112 std::is_same_v<CleanV, mapping_t<E>>,
113 "Type mismatch in Add: provided type does not match the expected type for this enum value");
114
115 typename Variant::variant_t variant;
116 variant.template emplace<Variant::Index(E)>(v);
117 m_data.emplace(E, std::move(variant));
118 }
119
120 // Runtime version of Add that takes the enum as a parameter.
121 template <typename V>
122 void Add(Enum e, V&& v)
123 {
124 if constexpr (Callback)
125 {
126 Callback(this, e, EnumBasedVariantMapAction::Add);
127 }
128
129 // Check if the type matches the SPECIFIC enum value at compile time if possible
130 using CleanV = std::remove_cvref_t<V>;
131
132 // Pre-check if this type matches the specific enum value being added to
133 if (!IsMatchingType<CleanV>(e))
134 {
135 THROW_HR_MSG(E_INVALIDARG, "Type mismatch: provided type does not match the expected type for enum value %d", static_cast<int>(e));
136 }
137
138 typename Variant::variant_t variant;
139 EmplaceAtRuntimeIndex(variant, e, std::forward<V>(v), std::make_index_sequence<static_cast<size_t>(Enum::Max)>());
140 m_data.emplace(e, std::move(variant));
141 }
142
143 // Runtime method to check if value V matches the mapped type for an enum value.
144 template <typename V>
145 bool IsMatchingType(Enum e) const
146 {
147 return IsMatchingTypeImpl<V>(e, std::make_index_sequence<static_cast<size_t>(Enum::Max)>());
148 }
149
150 // Return a value indicating whether the given enum has at least one entry.
151 bool Contains(Enum e) const
152 {
153 if constexpr (Callback)
154 {
155 Callback(this, e, EnumBasedVariantMapAction::Contains);
156 }
157 return (m_data.find(e) != m_data.end());
158 }
159
160 // Gets the count of values for a specific enum key.
161 size_t Count(Enum e) const
162 {
163 if constexpr (Callback)
164 {
165 Callback(this, e, EnumBasedVariantMapAction::Count);
166 }
167 return m_data.count(e);
168 }
169
170 // Gets the FIRST value for the enum key (for backward compatibility).
171 // Non-const version returns a reference that can be modified.
172 template <Enum E>
173 mapping_t<E>& Get()
174 {
175 if constexpr (Callback)
176 {
177 Callback(this, E, EnumBasedVariantMapAction::GetMutable);
178 }
179 auto itr = m_data.find(E);
180 THROW_HR_IF_MSG(E_NOT_SET, itr == m_data.end(), "Get(%d): key not found", static_cast<int>(E));
181
182 // Validate that the variant holds the expected type at the expected index
183 constexpr size_t expectedIndex = Variant::Index(E);
184 if (itr->second.index() != expectedIndex)
185 {
186 THROW_HR_MSG(
187 E_UNEXPECTED,
188 "Get(%d): variant type mismatch - expected index %zu, got %zu",
189 static_cast<int>(E),
190 expectedIndex,
191 itr->second.index());
192 }
193
194 return std::get<expectedIndex>(itr->second);
195 }
196
197 // Const overload of Get, cannot be modified.
198 template <Enum E>
199 const mapping_t<E>& Get() const
200 {
201 if constexpr (Callback)
202 {
203 Callback(this, E, EnumBasedVariantMapAction::Get);
204 }
205 auto itr = m_data.find(E);
206 THROW_HR_IF_MSG(E_NOT_SET, itr == m_data.cend(), "Get(%d): key not found", static_cast<int>(E));
207
208 // Validate that the variant holds the expected type at the expected index
209 constexpr size_t expectedIndex = Variant::Index(E);
210 if (itr->second.index() != expectedIndex)
211 {
212 THROW_HR_MSG(
213 E_UNEXPECTED,
214 "Get(%d): variant type mismatch - expected index %zu, got %zu",
215 static_cast<int>(E),
216 expectedIndex,
217 itr->second.index());
218 }
219
220 return std::get<expectedIndex>(itr->second);
221 }
222
223 // Gets ALL values for a specific enum key as a vector.
224 template <Enum E>
225 std::vector<mapping_t<E>> GetAll() const
226 {
227 if constexpr (Callback)
228 {
229 Callback(this, E, EnumBasedVariantMapAction::GetAll);
230 }
231
232 std::vector<mapping_t<E>> results;
233 auto range = m_data.equal_range(E);
234
235 for (auto it = range.first; it != range.second; ++it)
236 {
237 results.push_back(std::get<Variant::Index(E)>(it->second));
238 }
239
240 return results;
241 }
242
243 // Removes ALL entries for a specific enum key.
244 void Remove(Enum e)
245 {
246 if constexpr (Callback)
247 {
248 Callback(this, e, EnumBasedVariantMapAction::Remove);
249 }
250 m_data.erase(e);
251 }
252
253 // Gets the total number of items stored (across all keys).
254 size_t GetCount() const
255 {
256 return m_data.size();
257 }
258
259 // Gets a vector of all UNIQUE enum keys stored in the map.
260 std::vector<Enum> GetKeys() const
261 {
262 std::vector<Enum> keys;
263 Enum lastKey = static_cast<Enum>(-1);
264 bool first = true;
265
266 for (const auto& pair : m_data)
267 {
268 if (first || pair.first != lastKey)
269 {
270 keys.push_back(pair.first);
271 lastKey = pair.first;
272 first = false;
273 }
274 }
275
276 return keys;
277 }
278
279 private:
280 // Helper to implement runtime type checking.
281 template <typename V, size_t... I>
282 bool IsMatchingTypeImpl(Enum e, std::index_sequence<I...>) const
283 {
284 bool result = false;
285 ((static_cast<size_t>(e) == I ? (result = std::is_same_v<std::remove_cvref_t<V>, mapping_t<static_cast<Enum>(I)>>, true) : false) || ...);
286 return result;
287 }
288
289 // Helper to emplace at runtime-determined index
290 template <typename V, size_t... I>
291 void EmplaceAtRuntimeIndex(typename Variant::variant_t& variant, Enum e, V&& v, std::index_sequence<I...>)
292 {
293 size_t index = static_cast<size_t>(e) + 1;
294 bool handled = false;
295
296 (
297 [&] {
298 if (index == I + 1 && !handled)
299 {
300 using Emplacer = wsl::windows::wslc::EnumBasedVariantMapEmplacer<Enum, Mapping, V>;
301 Emplacer::template Emplace<I + 1>(variant, std::forward<V>(v));
302 handled = true;
303 }
304 }(),
305 ...);
306
307 if (!handled)
308 {
309 using CleanV = std::remove_cvref_t<V>;
310 THROW_HR_MSG(E_INVALIDARG, "Invalid enum value: %d", static_cast<int>(e));
311 }
312 }
313
314 std::multimap<Enum, typename Variant::variant_t> m_data;
315 };
316
317 // Helper for runtime emplacement into std::variant for EnumBasedVariantMap
318 template <typename Enum, template <Enum> typename Mapping, typename V>
319 struct EnumBasedVariantMapEmplacer
320 {
321 template <size_t Index>
322 static void Emplace(typename EnumBasedVariant<Enum, Mapping>::variant_t& variant, V&& value)
323 {
324 using TargetType = typename Mapping<static_cast<Enum>(Index - 1)>::value_t;
325 using CleanV = std::remove_cvref_t<V>;
326
327 constexpr bool is_same_type = std::is_same_v<CleanV, TargetType>;
328 constexpr bool is_convertible = std::is_convertible_v<CleanV, TargetType>;
329 constexpr bool is_constructible = std::is_constructible_v<TargetType, CleanV>;
330
331 if constexpr (is_same_type || is_convertible || is_constructible)
332 {
333 variant.template emplace<Index>(std::forward<V>(value));
334 }
335 else
336 {
337 throw std::runtime_error("Runtime type mismatch: cannot convert value to target type for this enum value");
338 }
339 }
340 };
341 } // namespace wsl::windows::wslc