FlagStateInterface implementors need only support being restored once.

PiperOrigin-RevId: 819030565
Change-Id: I92ac8ce4318f8d2e575c13752e490326030ba583

Author: sam-mccall

absl/flags/internal/commandlineflag.h

@@ -58,7 +58,7 @@ class FlagStateInterface {
   virtual ~FlagStateInterface();
 
   // Restores the flag originated this object to the saved state.
-  virtual void Restore() const = 0;
+  virtual void Restore() && = 0;
 };
 
 }  // namespace flags_internal

absl/flags/internal/flag.cc

@@ -26,6 +26,7 @@
 #include <memory>
 #include <string>
 #include <typeinfo>
+#include <utility>
 #include <vector>
 
 #include "absl/base/attributes.h"
@@ -139,8 +140,8 @@ class FlagState : public flags_internal::FlagStateInterface {
   friend class FlagImpl;
 
   // Restores the flag to the saved state.
-  void Restore() const override {
-    if (!flag_impl_.RestoreState(*this)) return;
+  void Restore() && override {
+    if (!std::move(flag_impl_).RestoreState(*this)) return;
 
     ABSL_INTERNAL_LOG(INFO,
                       absl::StrCat("Restore saved value of ", flag_impl_.Name(),

absl/flags/reflection.cc

@@ -19,6 +19,7 @@
 
 #include <atomic>
 #include <string>
+#include <utility>
 
 #include "absl/base/config.h"
 #include "absl/base/no_destructor.h"
@@ -320,9 +321,9 @@ class FlagSaverImpl {
   }
 
   // Restores the saved flag states into the flag registry.
-  void RestoreToRegistry() {
+  void RestoreToRegistry() && {
     for (const auto& flag_state : backup_registry_) {
-      flag_state->Restore();
+      std::move(*flag_state).Restore();
     }
   }
 
@@ -340,7 +341,7 @@ FlagSaver::FlagSaver() : impl_(new flags_internal::FlagSaverImpl) {
 FlagSaver::~FlagSaver() {
   if (!impl_) return;
 
-  impl_->RestoreToRegistry();
+  std::move(*impl_).RestoreToRegistry();
   delete impl_;
 }