Question

I recently saw a declaration of enum that looks like this:

<Serializable()>
<Flags()>
Public Enum SiteRoles

    ADMIN = 10 << 0
    REGULAR = 5 << 1
    GUEST = 1 << 2

End Enum

I was wondering if someone can explain what does “<<” syntax do or what it is used for? Thank you…

Answer 1

These are bitwise shift operations. Bitwise shifts are used to transform the integer value of the enum mebers here to a different number. Each enum member will actually have the bit-shifted value. This is probably an obfuscation technique and is the same as setting a fixed integer value for each enum member.

Each integer has a binary reprsentation (like 0111011); bit shifting allows bits to move to the left (<<) or right (>>) depending on which operator is used.

For example:

10 << 0 means:
1010 (10 in binary form) moved with 0 bits left is 1010

5 << 1 means:
101 (5 in binary form) moved one bit to the left = 1010 (added a zero to the right)
so 5 << 1 is 10 (because 1010 represents the number 10)

and etc.

In general the x << y operation can be seen as a fast way to calculate x * Pow(2, y);

You can read this article for more detailed info on bit shifting in .NET http://www.blackwasp.co.uk/CSharpShiftOperators.aspx