fix: eliminate unnecessary string copies in EmitDeref and GetOrMaterialize

- Change EmitDeref's `inner` parameter from `std::string` to `std::string_view`
  to avoid copying a string that is only ever read via StrCat.
  Update the three call sites accordingly (two std::move calls become plain refs).
- Change GetOrMaterialize's `materialize_fn` parameter from by-value to
  `const std::function<...>&` to avoid copying the callable object on each call.

Agent-Logs-Url: https://github.com/Cpp2Rust/cpp2rust/sessions/a4a77a6f-20a8-49a8-98d1-507851373647

Co-authored-by: nunoplopes <2998477+nunoplopes@users.noreply.github.com>

Author: Copilot

cpp2rust/converter/converter.cpp

@@ -2321,7 +2321,7 @@ bool Converter::VisitDeclRefExpr(clang::DeclRefExpr *expr) {
 
   if (decl->getType()->getAs<clang::ReferenceType>() && !isAddrOf() &&
       !map_iter_decls_.contains(clang::dyn_cast<clang::VarDecl>(decl))) {
-    EmitDeref(std::move(str), decl->getType().getNonReferenceType());
+    EmitDeref(str, decl->getType().getNonReferenceType());
     SetValueFreshness(expr->getType());
     return false;
   }
@@ -2464,7 +2464,7 @@ bool Converter::VisitMemberExpr(clang::MemberExpr *expr) {
   }
 
   if (!isAddrOf() && member->getType()->isReferenceType()) {
-    EmitDeref(std::move(str), member->getType().getNonReferenceType());
+    EmitDeref(str, member->getType().getNonReferenceType());
     return false;
   }
 
@@ -3561,14 +3561,14 @@ void Converter::ConvertAddrOf(clang::Expr *expr, clang::QualType pointer_type) {
   }
 }
 
-void Converter::EmitDeref(std::string inner, clang::QualType pointee_type) {
+void Converter::EmitDeref(std::string_view inner, clang::QualType pointee_type) {
   auto wrap = std::exchange(autoref_mut_, std::nullopt);
   PushParen outer(*this, wrap.has_value());
   if (wrap) {
     StrCat(*wrap ? "&mut" : "&");
   }
   PushParen paren(*this);
-  StrCat(GetPointerDerefPrefix(pointee_type), std::move(inner));
+  StrCat(GetPointerDerefPrefix(pointee_type), inner);
 }
 
 void Converter::ConvertDeref(clang::Expr *expr) {
@@ -3605,9 +3605,9 @@ Converter::CollectPrvalueToLRefArgs(clang::CallExpr *expr) {
 
 const std::string &Converter::TempMaterializationCtx::GetOrMaterialize(
     unsigned argument_num,
-    std::function<std::pair<std::string, std::string>(const std::string &,
-                                                      clang::QualType)>
-        materialize_fn) {
+    const std::function<std::pair<std::string, std::string>(const std::string &,
+                                                            clang::QualType)>
+        &materialize_fn) {
   auto &str = materialized_refs_.at(argument_num);
   if (!str.empty()) {
     return str;

cpp2rust/converter/converter.h

@@ -168,9 +168,8 @@ class Converter : public clang::RecursiveASTVisitor<Converter> {
 
     const std::string &GetOrMaterialize(
         unsigned argument_num,
-        std::function<std::pair<std::string, std::string>(const std::string &,
-                                                          clang::QualType)>
-            materialize_fn);
+        const std::function<std::pair<std::string, std::string>(
+            const std::string &, clang::QualType)> &materialize_fn);
 
   private:
     std::vector<std::string> materialized_refs_;
@@ -476,7 +475,7 @@ class Converter : public clang::RecursiveASTVisitor<Converter> {
 
   virtual void ConvertDeref(clang::Expr *expr);
 
-  void EmitDeref(std::string inner, clang::QualType pointee_type);
+  void EmitDeref(std::string_view inner, clang::QualType pointee_type);
 
   virtual void ConvertArrow(clang::Expr *expr);