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+.. title:: clang-tidy - performance-implicit-conversion-in-loop
+
+performance-implicit-conversion-in-loop
+=======================================
+
+This warning appears in a range-based loop with a loop variable of const ref
+type where the type of the variable does not match the one returned by the
+iterator. This means that an implicit conversion happens, which can for example
+result in expensive deep copies.
+
+Example:
+
+.. code-block:: c++
+
+  map<int, vector<string>> my_map;
+  for (const pair<int, vector<string>>& p : my_map) {}
+  // The iterator type is in fact pair<const int, vector<string>>, which means
+  // that the compiler added a conversion, resulting in a copy of the vectors.
+
+The easiest solution is usually to use ``const auto&`` instead of writing the
+type manually.