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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 do you create a 'flags' enum that supports combining multiple values using bitwise operations? How does the [Flags] attribute change the output of ToString() on a combined flags enum value? 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

What is the performance consideration when using Enum.HasFlag() versus a direct bitwise AND check?

Intermediate

Answer

Enum.HasFlag() involves BOXING the enum value (converting it to an object) internally in older .NET versions, making it measurably slower than a direct bitwise AND comparison in performance-sensitive, high-frequency code — modern .NET has optimized this significantly, but the direct bitwise check remains marginally faster and avoids any boxing concern entirely.
[Flags]
public enum Permissions { None = 0, Read = 1, Write = 2 }
var perms = Permissions.Read;

// Slightly slower historically (boxing), but more readable
bool hasRead1 = perms.HasFlag(Permissions.Read);

// Faster, no boxing, less readable
bool hasRead2 = (perms & Permissions.Read) == Permissions.Read;
Real-world example Choosing the direct bitwise check over HasFlag() specifically in a tight, performance-critical loop checking permissions millions of times.

Common follow-ups: At what call frequency does this performance difference actually become practically noticeable in a real application?

Memory & Garbage Collection
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