Question

We obviously can’t make everything constexpr. And if we don’t make anything constexpr, well, there won’t be any big problems. Lots of code have been written without it so far.

But is it a good idea to slap constexpr in anything that can possibly have it? Is there any potential problem with this?

Answer 1

It won’t bother the compiler. The compiler will (or should anyway) give you a diagnostic when/if you use it on code that doesn’t fit the requirements of a constexpr.

At the same time, I’d be a bit hesitant to just slap it on there because you could. Even though it doesn’t/won’t bother the compiler, your primary audience is other people reading the code. At least IMO, you should use constexpr to convey a fairly specific meaning to them, and just slapping it on other expressions because you can will be misleading. I think it would be fair for a reader to wonder what was going on with a function that’s marked as a constexpr, but only used as a normal run-time function.

At the same time, if you have a function that you honestly expect to use at compile time, and you just haven’t used it that way yet, marking it as constexpr might make considerably more sense.