C++的enum的语法

// These are exact duplicates of the real protobuf types, defined here since we can't include the protobuf headers
enum AttributeProto_AttributeType : int {
  AttributeProto_AttributeType_UNDEFINED = 0,
  AttributeProto_AttributeType_FLOAT = 1,
  AttributeProto_AttributeType_INT = 2,
  AttributeProto_AttributeType_STRING = 3,
  AttributeProto_AttributeType_TENSOR = 4,
  AttributeProto_AttributeType_GRAPH = 5,
  AttributeProto_AttributeType_SPARSE_TENSOR = 11,
  AttributeProto_AttributeType_FLOATS = 6,
  AttributeProto_AttributeType_INTS = 7,
  AttributeProto_AttributeType_STRINGS = 8,
  AttributeProto_AttributeType_TENSORS = 9,
  AttributeProto_AttributeType_GRAPHS = 10,
  AttributeProto_AttributeType_SPARSE_TENSORS = 12
};