Overloading Functions Based on Constexpr Arguments

In C 11, the inability to overload functions based on whether their arguments are constexpr has been a limiting factor in the usefulness of constexpr. This limitation prevents the creation of separate function definitions with the same signature, one for constexpr arguments and another for non-constexpr arguments.

Arguments for Constexpr Overloading

Consider a scenario where a function maps an enum to a std::string. An efficient implementation would involve creating an array of std::strings at compile time. However, since constexpr functions cannot construct objects, the existing constexpr implementation requires the creation of std::strings on every call, resulting in slower performance. A constexpr-specific overload would allow for the creation of std::strings at compile time, increasing efficiency.

Another example involves implementing a Fibonacci function with potential optimizations based on whether the argument is constexpr or not. For a constexpr argument, the function could perform no operation, while for a non-constexpr argument, it could utilize memoization to improve runtime performance.

Technical Feasibility

Overloading functions based on constexpr arguments is technically possible in C 11, although it would require extending the standard. As of now, the behavior of constexpr functions is strictly defined, and there is no mechanism for differentiating between constexpr and non-constexpr arguments in function overloading.

Conclusion

While constexpr overloading would enhance the functionality and efficiency of constexpr functions, its implementation would require a change in the C 11 standard. The absence of this feature has prompted developers to use workarounds such as function templates, but these solutions fall short of providing the same level of convenience and flexibility as overloadable constexpr functions.