Con.1 Issue #1905 Return local const (#2114)

* Con.1 const return

* minor

CppCoreGuidelines.md

@@ -16859,19 +16859,28 @@ Prevents accidental or hard-to-notice change of value.
 
     for (int i : c) cout << i << '\n';          // BAD: just reading
 
-##### Exception
+##### Exceptions
+
+A local variable that is returned by value and is cheaper to move than copy should not be declared `const`
+because it can force an unnecessary copy.
+
+    std::vector<int> f(int i)
+    {
+        std::vector<int> v{ i, i, i };  // const not needed
+        return v;
+    }
 
 Function parameters passed by value are rarely mutated, but also rarely declared `const`.
 To avoid confusion and lots of false positives, don't enforce this rule for function parameters.
 
-    void f(const char* const p); // pedantic
     void g(const int i) { ... }  // pedantic
 
 Note that a function parameter is a local variable so changes to it are local.
 
 ##### Enforcement
 
-* Flag non-`const` variables that are not modified (except for parameters to avoid many false positives)
+* Flag non-`const` variables that are not modified (except for parameters to avoid many false positives
+and returned local variables)
 
 ### <a name="Rconst-fct"></a>Con.2: By default, make member functions `const`