What are the Performance and Type Limitations of C# Switch Statements?

Limitations Analysis of C# Switch Statement

Although C#’s switch statement provides a convenient and easy-to-use method of program flow control, it also has some specific limitations:

Integer switch expression

The case expression of the switch statement must be an integer value, that is, a basic data type. This limitation arises from the underlying Common Intermediate Language (CIL) switch instruction, which requires a jump table mechanism.

Adjacent Case Statements

Adjacent case statements with consecutive integer values ​​allow efficient CIL switch implementation via jump tables. However, non-adjacent cases reduce efficiency, possibly leading to if-else-if structures or binary tree searches.

Performance impact

The performance of switch statements in C# depends on the compiler's optimization and specific scenarios. Use CILDASM to confirm:

• The switch of adjacent cases uses CIL switch instructions, and the complexity is O(1).
• The switch of non-adjacent cases uses binary tree search, and the complexity is O(log n).
• Switches for sparse cases may require an initial lookup in the dictionary, introducing additional overhead.

String type exclusion

The switch statement cannot directly handle string case expressions. They often rely on dictionary-based lookups, which can impact performance.

Theoretical considerations

Some people may think that the switch statement should support any type and case expression. However, the trade-off between efficiency and maintainability makes the current design a reasonable compromise.

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