add MutableMemento and improve FileHolder

common/file_holder.cc

@@ -64,6 +64,7 @@ void FileHolder::SetUp() noexcept {
           auto ptag = std::exchange(tag_, mem->Save());
           if (ptag != tag_) {
             onChildMementoChange();
+            if (mem_) mem_->Commit();  // commit owner's memento
           }
         }
         onChildUpdate();

common/file_holder.hh

@@ -16,6 +16,7 @@
 #include "common/file_base.hh"
 #include "common/generic_watcher.hh"
 #include "common/memento.hh"
+#include "common/mutable_memento.hh"
 #include "common/yas_nf7.hh"
 #include "common/yas_std_variant.hh"
 
@@ -34,8 +35,13 @@ class FileHolder : public nf7::FileBase::Feature {
   using Entity = std::variant<
       std::monostate, nf7::File::Path, std::shared_ptr<nf7::File>>;
 
-  FileHolder(nf7::File& owner, std::string_view id) noexcept :
-      owner_(&owner), id_(id) {
+  FileHolder(nf7::File& owner, std::string_view id,
+             nf7::MutableMemento* mem = nullptr) noexcept :
+      owner_(&owner), mem_(mem), id_(id) {
+  }
+  FileHolder(nf7::File& owner, std::string_view id,
+             nf7::MutableMemento& mem) noexcept :
+      FileHolder(owner, id, &mem) {
   }
   FileHolder(const FileHolder&) = delete;
   FileHolder(FileHolder&&) = delete;
@@ -62,6 +68,7 @@ class FileHolder : public nf7::FileBase::Feature {
     SetUp();
 
     onEmplace();
+    if (mem_) mem_->Commit();
   }
   void Emplace(std::unique_ptr<nf7::File>&& f) noexcept {
     TearDown();
@@ -70,6 +77,7 @@ class FileHolder : public nf7::FileBase::Feature {
     SetUp();
 
     onEmplace();
+    if (mem_) mem_->Commit();
   }
 
   nf7::File& GetFileOrThrow() {
@@ -108,7 +116,7 @@ class FileHolder : public nf7::FileBase::Feature {
     return own()? nf7::File::Path {{id_}}: std::get<nf7::File::Path>(entity_);
   }
 
-  // called when kUpdate event is caused by the child
+  // called when kUpdate event is happened on the child
   std::function<void(void)> onChildUpdate = [](){};
 
   // called when the child's memento tag id is changed
@@ -118,7 +126,9 @@ class FileHolder : public nf7::FileBase::Feature {
   std::function<void(void)> onEmplace = [](){};
 
  private:
-  nf7::File* const  owner_;
+  nf7::File*           const owner_;
+  nf7::MutableMemento* const mem_;
+
   const std::string id_;
 
   Entity entity_;

common/generic_memento.hh

@@ -7,13 +7,13 @@
 
 #include "nf7.hh"
 
-#include "common/memento.hh"
+#include "common/mutable_memento.hh"
 
 
 namespace nf7 {
 
 template <typename T>
-class GenericMemento : public nf7::Memento {
+class GenericMemento : public nf7::MutableMemento {
  public:
   class CustomTag;
 
@@ -45,12 +45,12 @@ class GenericMemento : public nf7::Memento {
     onRestore();
     if (file_) file_->Touch();
   }
-  void Commit() noexcept {
+  void Commit() noexcept override {
     tag_ = nullptr;
     onCommit();
     if (file_) file_->Touch();
   }
-  void CommitAmend() noexcept {
+  void CommitAmend() noexcept override {
     if (!tag_) return;
     auto itr = map_.find(tag_->id());
     assert(itr != map_.end());

common/mutable_memento.hh

@@ -0,0 +1,20 @@
+#pragma once
+
+#include "common/memento.hh"
+
+
+namespace nf7 {
+
+class MutableMemento : public nf7::Memento {
+ public:
+  MutableMemento() = default;
+  MutableMemento(const MutableMemento&) = delete;
+  MutableMemento(MutableMemento&&) = delete;
+  MutableMemento& operator=(const MutableMemento&) = delete;
+  MutableMemento& operator=(MutableMemento&&) = delete;
+
+  virtual void Commit() noexcept = 0;
+  virtual void CommitAmend() noexcept = 0;
+};
+
+}  // namespace nf7