add antlr

lib/antlr4/include/atn/SingletonPredictionContext.h

@@ -0,0 +1,36 @@
+/* Copyright (c) 2012-2017 The ANTLR Project. All rights reserved.
+ * Use of this file is governed by the BSD 3-clause license that
+ * can be found in the LICENSE.txt file in the project root.
+ */
+
+#pragma once
+
+#include "atn/PredictionContext.h"
+
+namespace antlr4 {
+namespace atn {
+
+  class ANTLR4CPP_PUBLIC SingletonPredictionContext : public PredictionContext {
+  public:
+    // Usually a parent is linked via a weak ptr. Not so here as we have kinda reverse reference chain.
+    // There are no child contexts stored here and often the parent context is left dangling when it's
+    // owning ATNState is released. In order to avoid having this context released as well (leaving all other contexts
+    // which got this one as parent with a null reference) we use a shared_ptr here instead, to keep those left alone
+    // parent contexts alive.
+    const Ref<PredictionContext> parent;
+    const size_t returnState;
+
+    SingletonPredictionContext(Ref<PredictionContext> const& parent, size_t returnState);
+    virtual ~SingletonPredictionContext();
+
+    static Ref<SingletonPredictionContext> create(Ref<PredictionContext> const& parent, size_t returnState);
+
+    virtual size_t size() const override;
+    virtual Ref<PredictionContext> getParent(size_t index) const override;
+    virtual size_t getReturnState(size_t index) const override;
+    virtual bool operator == (const PredictionContext &o) const override;
+    virtual std::string toString() const override;
+  };
+
+} // namespace atn
+} // namespace antlr4