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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?
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A constexpr integral value can be used wherever a const integer is required, such as in template arguments and array declarations. And when a value is computed at compile time instead of run time, it helps your program run faster and use less memory.
In other words, you should use constexpr for your constants in header files, if possible, otherwise const . And if you require the address of that constant to be the same everywhere mark it as inline .
const applies for variables, and prevents them from being modified in your code. constexpr tells the compiler that this expression results in a compile time constant value, so it can be used in places like array lengths, assigning to const variables, etc.
Understanding constexpr Specifier in C++ constexpr is a feature added in C++ 11. The main idea is a performance improvement of programs by doing computations at compile time rather than run time.
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.
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