Add libbabeltrace2 C++ interface base

[babeltrace.git] / src / cpp-common / bt2 / internal / borrowed-obj.hpp

diff --git a/src/cpp-common/bt2/internal/borrowed-obj.hpp b/src/cpp-common/bt2/internal/borrowed-obj.hpp
new file mode 100644 (file)
index 0000000..89feb62
--- /dev/null
+++ b/src/cpp-common/bt2/internal/borrowed-obj.hpp
@@ -0,0 +1,124 @@
+/*
+ * Copyright 2019-2020 (c) Philippe Proulx <pproulx@efficios.com>
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#ifndef BABELTRACE_CPP_COMMON_BT2_INTERNAL_BORROWED_OBJ_HPP
+#define BABELTRACE_CPP_COMMON_BT2_INTERNAL_BORROWED_OBJ_HPP
+
+#include <type_traits>
+
+#include "common/assert.h"
+
+namespace bt2 {
+namespace internal {
+
+template <typename ObjT, typename LibObjT, typename RefFuncsT>
+class SharedObj;
+
+/*
+ * An instance of this class wraps a pointer to a libbabeltrace2 object
+ * of type `LibObjT` without managing any reference counting.
+ *
+ * This is an abstract base class for any libbabeltrace2 object wrapper.
+ *
+ * `LibObjT` is the direct libbabeltrace2 object type, for example
+ * `bt_stream_class` or `const bt_value`.
+ *
+ * Methods of a derived class can call _libObjPtr() to access the
+ * libbabeltrace2 object pointer.
+ */
+template <typename LibObjT>
+class BorrowedObj
+{
+    static_assert(!std::is_pointer<LibObjT>::value, "`LibObjT` must not be a pointer");
+
+    /*
+     * This makes it possible for a `BorrowedObj<const bt_something>`
+     * instance to get assigned an instance of
+     * `BorrowedObj<bt_something>` (copy constructor and assignment
+     * operator).
+     *
+     * C++ forbids the other way around.
+     */
+    template <typename AnyLibObjT>
+    friend class BorrowedObj;
+
+    /*
+     * This is to allow a `SharedObj<_ThisBorrowedObj, LibObjT, ...>`
+     * instance containing a `BorrowedObj<LibObjT>` instance to access
+     * _libObjPtr() in order to increment/decrement its libbabeltrace2
+     * reference count.
+     */
+    template <typename ObjT, typename AnyLibObjT, typename RefFuncsT>
+    friend class SharedObj;
+
+protected:
+    // libbabeltrace2 object pointer
+    using _LibObjPtr = LibObjT *;
+
+    // This complete borrowed object
+    using _ThisBorrowedObj = BorrowedObj<LibObjT>;
+
+    /*
+     * Builds a borrowed object to wrap the libbabeltrace2 object
+     * pointer `libObjPtr`.
+     *
+     * `libObjPtr` must not be `nullptr`.
+     */
+    explicit BorrowedObj(const _LibObjPtr libObjPtr) noexcept : _mLibObjPtr {libObjPtr}
+    {
+        BT_ASSERT(libObjPtr);
+    }
+
+    /*
+     * Generic copy constructor.
+     *
+     * This converting constructor accepts both an instance of
+     * `_ThisBorrowedObj` and an instance (`other`) of
+     * `BorrowedObj<ConstLibObjT>`, where `ConstLibObjT` is the `const`
+     * version of `LibObjT`, if applicable.
+     *
+     * This makes it possible for a `BorrowedObj<const bt_something>`
+     * instance to be built from an instance of
+     * `BorrowedObj<bt_something>`. C++ forbids the other way around.
+     */
+    template <typename OtherLibObjT>
+    BorrowedObj(const BorrowedObj<OtherLibObjT>& other) noexcept : BorrowedObj {other._mLibObjPtr}
+    {
+    }
+
+    /*
+     * Generic assignment operator.
+     *
+     * This operator accepts both an instance of
+     * `_ThisBorrowedObj` and an instance (`other`) of
+     * `BorrowedObj<ConstLibObjT>`, where `ConstLibObjT` is the `const`
+     * version of `LibObjT`, if applicable.
+     *
+     * This makes it possible for a `BorrowedObj<const bt_something>`
+     * instance to get assigned an instance of
+     * `BorrowedObj<bt_something>`. C++ forbids the other way around.
+     */
+    template <typename OtherLibObjT>
+    _ThisBorrowedObj& operator=(const BorrowedObj<OtherLibObjT>& other) noexcept
+    {
+        _mLibObjPtr = other._mLibObjPtr;
+        return *this;
+    }
+
+    // Wrapped libbabeltrace2 object pointer
+    _LibObjPtr _libObjPtr() const noexcept
+    {
+        return _mLibObjPtr;
+    }
+
+private:
+    _LibObjPtr _mLibObjPtr;
+};
+
+} // namespace internal
+} // namespace bt2
+
+#endif // BABELTRACE_CPP_COMMON_BT2_INTERNAL_BORROWED_OBJ_HPP