[llvm] [llvm][ADT] Structured bindings for move-only types in `StringMap` (PR #114676)

[Jakub Kuderski via llvm-commits]

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@@ -147,25 +147,57 @@ class StringMapEntry final : public StringMapEntryStorage<ValueTy> {
 };
 
 // Allow structured bindings on StringMapEntry.
+
+namespace detail {
+template <std::size_t Index> struct StringMapEntryGet;
+
+template <> struct StringMapEntryGet<0> {
+  template <typename ValueTy> static StringRef get(StringMapEntry<ValueTy> &E) {
+    return E.getKey();
+  }
+
+  template <typename ValueTy>
+  static StringRef get(const StringMapEntry<ValueTy> &E) {
+    return E.getKey();
+  }
+};
+
+template <> struct StringMapEntryGet<1> {
+  template <typename ValueTy> static ValueTy &get(StringMapEntry<ValueTy> &E) {
+    return E.getValue();
+  }
+
+  template <typename ValueTy>
+  static const ValueTy &get(const StringMapEntry<ValueTy> &E) {
+    return E.getValue();
+  }
+};
+} // namespace detail
+
+template <std::size_t Index, typename ValueTy>
+decltype(auto) get(StringMapEntry<ValueTy> &E) {
+  return detail::StringMapEntryGet<Index>::get(E);
+}
+
 template <std::size_t Index, typename ValueTy>
 decltype(auto) get(const StringMapEntry<ValueTy> &E) {
-  static_assert(Index < 2);
-  if constexpr (Index == 0)
-    return E.first();
-  else
-    return E.second;
+  return detail::StringMapEntryGet<Index>::get(E);
 }
 
 } // end namespace llvm
 
-namespace std {
 template <typename ValueTy>
-struct tuple_size<llvm::StringMapEntry<ValueTy>>
+struct std::tuple_size<llvm::StringMapEntry<ValueTy>>
     : std::integral_constant<std::size_t, 2> {};
 
-template <std::size_t I, typename ValueTy>
-struct tuple_element<I, llvm::StringMapEntry<ValueTy>>
-    : std::conditional<I == 0, llvm::StringRef, ValueTy> {};
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kuhar wrote:

we can use pair instead of tuple, I think

https://github.com/llvm/llvm-project/pull/114676