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How do you declare an enum in C#, and what underlying type do its members have by default? How do you convert between an enum value and its underlying numeric value, and between an enum and its string name? How does the [Flags] attribute change the output of ToString() on a combined flags enum value? What is the performance consideration when using Enum.HasFlag() versus a direct bitwise AND check? How would you write an extension method to safely add or remove a specific flag from a [Flags] enum value without manual bitwise operators scattered throughout your code? How do you safely validate that an enum value received from external input (like deserialized JSON or a database) is actually a DEFINED member, given that enums don't enforce this by default? How would you use pattern matching (switch expressions) with an enum, including exhaustiveness warnings from the compiler? How do enums interact with generic constraints, and why has it historically been awkward to write generic, reusable flag-manipulation code? How would you design an enum-based state machine using pattern matching to enforce valid state transitions at compile time or runtime?
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C# › Enums & Flags

How do you create a 'flags' enum that supports combining multiple values using bitwise operations?

Intermediate

Answer

Mark the enum with [Flags] and assign each member a distinct POWER-OF-TWO value, letting you safely combine multiple flags into a single value with the bitwise OR operator and check for a specific flag's presence with bitwise AND.
[Flags]
public enum Permissions {
  None = 0,
  Read = 1,
  Write = 2,
  Delete = 4,
  All = Read | Write | Delete
}
Permissions userPerms = Permissions.Read | Permissions.Write;
bool canWrite = (userPerms & Permissions.Write) == Permissions.Write; // true
Real-world example Modeling a user's combined set of permissions (read/write/delete) compactly as a single stored enum value.

Common follow-ups: What does the [Flags] attribute actually change about the enum's behavior beyond just documentation intent?

Attributes & Reflection
All 10 Enums & Flags questions