Re: BOOST_IS_CONSTANT_EVALUATED_INT(integer-expression)(integer-expression)

From: John Maddock (jz.maddock_at_[hidden])
Date: 2021-08-23 17:20:39

On 23/08/2021 00:36, Ivan Matek via Boost wrote:
> On Sun, Aug 22, 2021 at 10:29 PM Robert Ramey via Boost <
> boost_at_[hidden]> wrote:
>
>> Yes.... but the function should really return the same value in both
>> constexpr and runtime usage.
>>
>> LOL - for me, the whole point of this is to use a different value
>> depending on whether or not the value is known at compile time. Maybe
>> someone wants to opine on this.
>>
> I think it would help discussion if you or John could provide a complete
> use case when different result is desired for a function depending on if it
> is running at compile time or not?

I could be wrong, but I don't believe that that would be a valid use 
case, like you, the intended usage is to optimize runtime and compile 
time usage, ie:

constexpr int f(int i)

{

 Â  if(std::is_constant_evaluated())

 Â  {

 Â Â Â Â Â Â  // constexpr friendly code here

 Â  }

 Â  else

 Â  {

 Â Â Â  // Maybe use a function that's super fast but not constexpr safe

 Â  }

}

John.

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