C# binary literals

Update

C# 7.0 now has binary literals, which is awesome.

[Flags]
enum Days
{
    None = 0,
    Sunday    = 0b0000001,
    Monday    = 0b0000010,   // 2
    Tuesday   = 0b0000100,   // 4
    Wednesday = 0b0001000,   // 8
    Thursday  = 0b0010000,   // 16
    Friday    = 0b0100000,   // etc.
    Saturday  = 0b1000000,
    Weekend = Saturday | Sunday,
    Weekdays = Monday | Tuesday | Wednesday | Thursday | Friday
}

Original Post

Since the topic seems to have turned to declaring bit-based flag values in enums, I thought it would be worth pointing out a handy trick for this sort of thing. The left-shift operator (<<) will allow you to push a bit to a specific binary position. Combine that with the ability to declare enum values in terms of other values in the same class, and you have a very easy-to-read declarative syntax for bit flag enums.

[Flags]
enum Days
{
    None        = 0,
    Sunday      = 1,
    Monday      = 1 << 1,   // 2
    Tuesday     = 1 << 2,   // 4
    Wednesday   = 1 << 3,   // 8
    Thursday    = 1 << 4,   // 16
    Friday      = 1 << 5,   // etc.
    Saturday    = 1 << 6,
    Weekend     = Saturday | Sunday,
    Weekdays    = Monday | Tuesday | Wednesday | Thursday | Friday
}

C# 7.0 supports binary literals (and optional digit separators via underscore characters).

An example:

int myValue = 0b0010_0110_0000_0011;

You can also find more information on the Roslyn GitHub page.

Only integer and hex directly, I'm afraid (ECMA 334v4):

9.4.4.2 Integer literals Integer literals are used to write values of types int, uint, long, and ulong. Integer literals have two possible forms: decimal and hexadecimal.

To parse, you can use:

int i = Convert.ToInt32("01101101", 2);