Why Are C# Switch Statements Limited to Integral Types and Constant Case Expressions?

Restrictions of C# switch statement

C#'s switch statement has two obvious limitations: it cannot handle values ​​of non-integer types, and the case expression must be a constant. This raises questions about the reasons behind these restrictions.

Reasons for integer switch values

C#'s switch statement is implemented using the CIL switch instruction, which is a jump table that requires an index pointing to a set of jump addresses. Jump tables are efficient when the case values ​​are consecutive, but less efficient when they are not.

For discontinuous expressions, the compiler must use linear if-else checks or binary tree searches. This can cause performance degradation.

Reasons for constant case expressions

The CIL switch instruction requires a constant as its index in the jump table. This ensures that the jump table is created at compile time and not at run time.

Non-const case expressions will require a jump table to be created at runtime, which will be inefficient and may lead to security vulnerabilities.

Impact on performance

The performance impact of these limitations will depend on the specific scenario. Due to the use of CIL switch instructions, continuous case expressions are generally faster than discontinuous expressions.

Using strings or other complex objects in switch statements also affects performance because the compiler may have to create a dictionary or hash table to map the values ​​to the corresponding jump addresses.

Conclusion

The limitations of the C# switch statement are mainly due to performance and security considerations. Although these restrictions may impose some constraints on the use of switch statements, they are necessary to ensure efficient and safe code execution.

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