3 files changed, 44 insertions, 39 deletions

diff --git a/src/Document.cxx b/src/Document.cxx
index b5ec9a275..24ddd04ce 100644
--- a/src/Document.cxx
+++ b/src/Document.cxx
@@ -51,6 +51,16 @@
 using namespace Scintilla;
 using namespace Scintilla::Internal;
 
+LexInterface::LexInterface(Document *pdoc_) noexcept : pdoc(pdoc_), performingStyle(false) {
+}
+
+LexInterface::~LexInterface() noexcept = default;
+
+void LexInterface::SetInstance(ILexer5 *instance_) {
+	instance.reset(instance_);
+	pdoc->LexerChanged();
+}
+
 void LexInterface::Colourise(Sci::Position start, Sci::Position end) {
 	if (pdoc && instance && !performingStyle) {
 		// Protect against reentrance, which may occur, for example, when
@@ -86,6 +96,10 @@ LineEndType LexInterface::LineEndTypesSupported() {
 	return LineEndType::Default;
 }
 
+bool LexInterface::UseContainerLexing() const noexcept {
+	return !instance;
+}
+
 ActionDuration::ActionDuration(double duration_, double minDuration_, double maxDuration_) noexcept :
 	duration(duration_), minDuration(minDuration_), maxDuration(maxDuration_) {
 }
diff --git a/src/Document.h b/src/Document.h
index 7984ad018..e2962b4a3 100644
--- a/src/Document.h
+++ b/src/Document.h
@@ -164,21 +164,41 @@ public:
 	bool isEnabled;
 };
 
+struct LexerReleaser {
+	// Called by unique_ptr to destroy/free the Resource
+	void operator()(Scintilla::ILexer5 *pLexer) noexcept {
+		if (pLexer) {
+			try {
+				pLexer->Release();
+			} catch (...) {
+				// ILexer5::Release must not throw, ignore if it does.
+			}
+		}
+	}
+};
+
+using LexerInstance = std::unique_ptr<Scintilla::ILexer5, LexerReleaser>;
+
+// LexInterface defines the interface to ILexer used in Document.
+// The LexState subclass is actually created and that is used within ScintillaBase
+// to provide more methods that are exposed through Scintilla's external API.
 class LexInterface {
 protected:
 	Document *pdoc;
-	Scintilla::ILexer5 *instance;
+	LexerInstance instance;
 	bool performingStyle;	///< Prevent reentrance
 public:
-	explicit LexInterface(Document *pdoc_) noexcept : pdoc(pdoc_), instance(nullptr), performingStyle(false) {
-	}
-	virtual ~LexInterface() {
-	}
+	explicit LexInterface(Document *pdoc_) noexcept;
+	// Deleted so LexInterface objects can not be copied.
+	LexInterface(const LexInterface &) = delete;
+	LexInterface(LexInterface &&) = delete;
+	LexInterface &operator=(const LexInterface &) = delete;
+	LexInterface &operator=(LexInterface &&) = delete;
+	virtual ~LexInterface() noexcept;
+	void SetInstance(ILexer5 *instance_);
 	void Colourise(Sci::Position start, Sci::Position end);
 	virtual Scintilla::LineEndType LineEndTypesSupported();
-	bool UseContainerLexing() const noexcept {
-		return instance == nullptr;
-	}
+	bool UseContainerLexing() const noexcept;
 };
 
 struct RegexError : public std::runtime_error {
diff --git a/src/ScintillaBase.cxx b/src/ScintillaBase.cxx
index 238299734..b2a15a286 100644
--- a/src/ScintillaBase.cxx
+++ b/src/ScintillaBase.cxx
@@ -550,13 +550,8 @@ namespace Scintilla::Internal {
 class LexState : public LexInterface {
 public:
 	explicit LexState(Document *pdoc_) noexcept;
-	void SetInstance(ILexer5 *instance_);
-	// Deleted so LexState objects can not be copied.
-	LexState(const LexState &) = delete;
-	LexState(LexState &&) = delete;
-	LexState &operator=(const LexState &) = delete;
-	LexState &operator=(LexState &&) = delete;
-	~LexState() override;
+
+	// LexInterface deleted the standard operators and defined the virtual destructor so don't need to here.
 
 	const char *DescribeWordListSets();
 	void SetWordList(int n, const char *wl);
@@ -592,30 +587,6 @@ public:
 LexState::LexState(Document *pdoc_) noexcept : LexInterface(pdoc_) {
 }
 
-LexState::~LexState() {
-	if (instance) {
-		try {
-			instance->Release();
-		} catch (...) {
-			// ILexer5::Release must not throw, ignore if it does.
-		}
-		instance = nullptr;
-	}
-}
-
-void LexState::SetInstance(ILexer5 *instance_) {
-	if (instance) {
-		try {
-			instance->Release();
-		} catch (...) {
-			// ILexer5::Release must not throw, ignore if it does.
-		}
-		instance = nullptr;
-	}
-	instance = instance_;
-	pdoc->LexerChanged();
-}
-
 LexState *ScintillaBase::DocumentLexState() {
 	if (!pdoc->GetLexInterface()) {
 		pdoc->SetLexInterface(std::make_unique<LexState>(pdoc));