Enums

Jancy brings a couple of enhancements to the enumeration types as we know them in C/C++/Java.

In Jancy, traditional enums conceal member identifiers within their enum namespaces to prevent namespace pollution. Plus, Jancy enums can be derived from an integer type. This comes in handy when declaring fields of protocol headers.

enum IcmpType: uint8_t
{
    EchoReply               = 0,
    DestinationUnreachable  = 3,
    SourceQuench            = 4,
    Redirect                = 5,
    Echo                    = 8,
    RouterAdvertisement     = 9,
    RouterSelection         = 10,
    TimeExceeded            = 11,
    ParameterProblem        = 12,
    TimestampRequest        = 13,
    TimestampReply          = 14,
    InformationRequest      = 15,
    InformationReply        = 16,
    AddressMaskRequest      = 17,
    AddressMaskReply        = 18,
    TraceRoute              = 30,
}

Exposed Enums

To simplify porting existing C/C++ code into Jancy we offer an exposed enum variation, which behaves like a traditional C/C++ enum, i.e. it exposes the member identifier into the parent namespace.

exposed enum State
{
    State_Idle, // = 0
    State_Connecting,
    State_Connected,
    State_Disconnecting,
}

foo ()
{
    State state = State_Connecting; // State.State_Connecting is also ok
    state = 100; // error: cast int->enum must be explicit
}

Bitflag Enums

Jancy also features bitflag enums, which are enumerations dedicated to describing a set of bitflags. A bitflag enum differs from a regular enum in the following aspects:

  • It’s automatic value assignment sequence is 1, 2, 4, 8,… thus describing bit positions
  • Bitwise OR operator | on two operands of matching bitflag enum types yields the same bitflag enum type
  • Bitwise AND operator & on bitflag enum and integer yields the same bitflag enum type
  • It’s OK to assign 0 to a bitflag enum

Like Jancy enums, bitflag enums do not pollute the parent namespace.

bitflag enum OpenFlags
{
    ReadOnly,      // = 0x01
    Exclusive         = 0x20,
    DeleteOnClose, // = 0x40
}

foo ()
{
    OpenFlags flags = 0; // 0 is ok to assign to 'bitflag enum'

    flags = OpenFlags.ReadOnly | OpenFlags.Exclusive | OpenFlags.DeleteOnClose;
    flags &= ~OpenFlags.Exclusive;
    flags = 200; // error: cast int->bitflag enum must be explicit
}