================
@@ -0,0 +1,69 @@
+.. title:: clang-tidy - modernize-use-string-view
+
+modernize-use-string-view
+=========================
+
+Looks for functions returning ``std::[w|u8|u16|u32]string`` and suggests to
+change it to ``std::[...]string_view`` for performance reasons if possible.
+
+Each time a new ``std::string`` is created from a literal, a copy of that
+literal is allocated either in ``std::string``'s internal buffer
+(for short literals) or in a heap.
+
+For the cases where ``std::string`` is returned from a function,
+such allocations can sometimes be eliminated by using ``std::string_view``
+as a return type.
+
+This check looks for such functions returning ``std::string`` baked from the
+literals and suggests replacing their return type to ``std::string_view``.
+
+It handles ``std::string``, ``std::wstring``, ``std::u8string``,
+``std::u16string`` and ``std::u32string`` along with their aliases and selects
+the proper kind of ``std::string_view`` to return.
+
+Consider the following example:
+
+.. code-block:: c++
+
+ std::string foo(int i) {
+ switch(i) {
+ case 1:
+ return "case 1";
+ ...
+ default:
+ return "default";
+ }
+ }
+
+In the code above a new ``std::string`` object is created on each function
+invocation, making a copy of a string literal and possibly allocating a memory
+in a heap.
+
+The check gets this code transformed into:
+
+.. code-block:: c++
+
+ std::string_view foo(int i) {
+ switch(i) {
+ case 1:
+ return "case 1";
+ ...
+ default:
+ return "default";
+ }
+ }
+
+New version re-uses statically allocated literals without additional overhead.
+
+Options
+-------
+
+.. option:: IgnoredFunctions
+
+ A semicolon-separated list of the names of functions or methods to be
+ ignored. Regular expressions are accepted, e.g. ``[Rr]ef(erence)?$`` matches
+ every type with suffix ``Ref``, ``ref``, ``Reference`` and ``reference``.
+ The default is {``toString$;ToString$;to_string$;to_s$``}. If a
+ name in the list contains the sequence `::` it is matched against the
+ qualified type name (i.e. ``namespace::Type``), otherwise it is matched
+ against only the type name (i.e. ``Type``).
----------------
irishrover wrote:
Docs say qualified name can also be matched:
```
// Returns a matcher that matches NamedDecl's against a list of provided regular
// expressions. If a regular expression contains starts ':' the NamedDecl's
// qualified name will be used for matching, otherwise its name will be used.
inline ::clang::ast_matchers::internal::Matcher<NamedDecl>
matchesAnyListedName(llvm::ArrayRef<StringRef> NameList) {
return ::clang::ast_matchers::internal::Matcher(
new MatchesAnyListedNameMatcher(NameList));
}
```
https://github.com/llvm/llvm-project/pull/172170
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