What does the [Flags] Enum Attribute mean in C#?

The [Flags] attribute in C# is applied to an enum to treat its members as bit fields. This lets you combine enum values using bitwise operations (|, &, etc.) rather than treating them as a single choice. In practice, [Flags] helps you manage scenarios where multiple enum values could logically coexist at the same time.

How It Works

1. Bitwise Combinations
   Each enum member should be assigned a distinct bit in its underlying integer value—commonly powers of two. For example:

   [Flags]
   public enum FileAccess
   {
       Read   = 1,  // 0001
       Write  = 2,  // 0010
       Execute = 4, // 0100
       None   = 0
   }

   You can then combine values:

   FileAccess access = FileAccess.Read | FileAccess.Write;
   // access now has both Read (0001) and Write (0010) => 0011

2. Improved .ToString()
   When [Flags] is present, calling access.ToString() returns a comma-separated list of the active flags (e.g., "Read, Write").

3. Checking for Flags
   You can test if a specific flag is set using either bitwise operations or the built-in .HasFlag() method:

   if (access.HasFlag(FileAccess.Write))
   {
       // Do something with write access
   }

Why Use [Flags]?

• Logical Modeling: If multiple enum options can be enabled at once, [Flags] accurately represents that scenario.
• Cleaner Checks: Instead of tracking multiple booleans, a single enum with combined flags can simplify and centralize your code logic.
• Readability: [Flags] modifies the default .ToString() behavior to reflect all active bits, making debugging easier.

Tips and Best Practices

1. Use Powers of Two: Start with 1, 2, 4, 8, ... to avoid accidental overlaps.
2. Include a None/Zero: A None = 0 flag can signify “no value” for better clarity.
3. Use Meaningful Names: Make it clear which operations or states each bit stands for.

Strengthen Your C# Skills Further

Bitwise operations and [Flags] are one of many C# concepts you’ll see in interviews and real-world applications. If you’re looking to deepen your understanding of C# and coding patterns, consider the following courses at DesignGurus.io:

• Grokking the Coding Interview: Patterns for Coding Questions
• Grokking Data Structures & Algorithms for Coding Interviews

For additional tutorials and insights, check out the DesignGurus.io YouTube channel. By mastering [Flags] enums and other advanced language features, you’ll write clearer, more efficient, and more maintainable C# code.