Op 10-Oct-16 om 2:45 PM schreef smplx:
>
> On Mon, 10 Oct 2016, Wouter van Ooijen wrote:
>
>> In your idea, as a user, can I be *sure* that a certain (complicated)
>> part is run by the compiler at compilation?
>>
>> In C++ 0x14 you can
>>
>> - declare any function as constexper, which means that the compiler must
>> check that it can evaluate that function at compile time (provided that
>> it knows the arguments at compile time). Such a function is still usable
>> at run time too.
>>
>> - declare any const value as constexpr, which means that the compiler
>> must evaluate it at compile time.
>>
>> There isn't much special about a constexpr function that isn't obvious
>> (like: it can't access globals, can't do memory allocation, etc.).
> Hi Wouter,
>
> The short answer is yes - if you declare a constant and use a function to
> initalise it that does not depend on external unknowns.
>
> The longer answer is "it is not intended to be restricted that way". When
> I explained how functions could be executed at compile time this was an
> attempt to quickly focus the reader on an obvious benefit. The reallity
> however is that compile time execution goes way beyond what I described.
> It opens up a huge number of possibilites for deep analysis and
> optimisation which I have not described. It is not just about executing
> functions as a unit but about executing as much of the code as possible
> without the function call acting as a barrier.
>
> What I would like to see users doing is writing code that describes the
> process they need to achive and let the compiler worry about the
> optimisation.

IMO that sounds good, but it is what an optimizer should do anyway. On=20
top of that, you (as an application writer) want guarantees that certain=20
parts are pre-caclulated. That is not worrying, that is getting certainty.

wouter
--=20
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