src/developer/debug/zxdb/expr/found_member.h

// Copyright 2018 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef SRC_DEVELOPER_DEBUG_ZXDB_EXPR_FOUND_MEMBER_H_
#define SRC_DEVELOPER_DEBUG_ZXDB_EXPR_FOUND_MEMBER_H_

#include <stdint.h>

#include "src/developer/debug/zxdb/symbols/data_member.h"
#include "src/lib/fxl/memory/ref_ptr.h"

namespace zxdb {

// The result of finding a member in a collection.
//
// This class consists of a DataMember and a possible offset within the containing object of that
// DataMember.
//
// To actually resolve the value when the data_member is not static, the containing object needs to
// be known. Typically one would have an object, find a member on it (producing a FoundMember), and
// then use that object and the FoundMember to resolve its value.
//
// If the data member is static data_member()->is_external() will be set.
class FoundMember {
 public:
  FoundMember();

  // Constructs from a data member with no additional offset. This means the DataMember must be
  // a direct member of the collection it's referring to or it's external.
  explicit FoundMember(const DataMember* data_member);

  // Constructs from a data member and a computed offset. The data_member_offset will be used
  // instead of the data_member->member_location() which allows it to refer to members of derived
  // classes which may have an additional ofsfet within the containing structure.
  FoundMember(const DataMember* data_member, uint32_t data_member_offset);

  ~FoundMember();

  bool is_null() const { return !data_member_; }

  const DataMember* data_member() const { return data_member_.get(); }
  fxl::RefPtr<DataMember> data_member_ref() const { return data_member_; }

  // Offset of this member in the containing object.
  //
  // This is valid only for non-static members.
  //
  // Static members will have data_member()->is_external() set and this offset will not apply
  // (because there's no underlying object).
  uint32_t data_member_offset() const { return data_member_offset_; }

 private:
  // Variable member of the object_var_ that this class represents.
  //
  // NOTE: that this DataMember isn't necessarily a member of the original object that was queried.
  // It could be on a base class. In this case, the offset specified on the DataMember data member
  // will be incorrect since it refers to the offset within its enclosing class. Therefore, one
  // should always use the data_member_offset_ below.
  fxl::RefPtr<DataMember> data_member_;

  // The offset within object_var_ of the data_member_. This will take into account all derived
  // classes.
  uint32_t data_member_offset_ = 0;
};

}  // namespace zxdb

#endif  // SRC_DEVELOPER_DEBUG_ZXDB_EXPR_FOUND_MEMBER_H_