What are the limitations of constexpr in C++20?

What are the limitations of constexpr in C++20?

In C++20, constexpr has expanded significantly, but it still has limitations. For instance, not all functions can be evaluated at compile time, especially those involving dynamic memory allocation or certain types of I/O operations.

Can you give examples of functions that can't be constexpr?

Sure! Functions that perform dynamic memory allocation, like those using new or malloc, cannot be constexpr. Additionally, functions that rely on runtime information, such as those using std::cin, are also excluded.

What about constexpr with templates? Are there any restrictions?

Yes, while you can use constexpr with templates, there are restrictions. For example, template parameters must be known at compile time, and certain operations within the template must also be constexpr-compatible.

How does constexpr affect performance in C++?

Using constexpr can improve performance by allowing computations to be done at compile time, reducing runtime overhead. However, excessive use of complex constexpr functions can lead to longer compile times.