================
@@ -0,0 +1,99 @@
+.. 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.
+
+The check handles at least the following cases (``[w|u8|u16|u32]string`` are
+handled the same way but omitted for brevity):
+
+* ``return "simpleLiteral";``
+* ``return MACRO_LITERAL;``
+* ``return R"(simpleLiteral)";``
+* ``auto foo() -> std::string { return "literal"; }``
+* ``return std::string();``
+* ``return std::string{};``
+* ``return {};``
+* ``return flag ? "foo" : "bar";``
+* switch statements as in the sample above
+* simple macro typedefs for ``std::string``
+
----------------
vbvictor wrote:
We usually don't state positive examples in docs.
It can get complicated to keep docs in sync with behavoir when adding new
patches.
https://github.com/llvm/llvm-project/pull/172170
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