On Mon, 10 Oct 2016, Wouter van Ooijen wrote:

> 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 mus=
t
>>> check that it can evaluate that function at compile time (provided that
>>> it knows the arguments at compile time). Such a function is still usabl=
e
>>> 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 t=
o
>> initalise it that does not depend on external unknowns.
>>
>> The longer answer is "it is not intended to be restricted that way". Whe=
n
>> 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
> top of that, you (as an application writer) want guarantees that certain
> parts are pre-caclulated. That is not worrying, that is getting certainty=
..
>

Hi Wouter,

If you are saying that you want to be able to guarantee that calling a=20
function at a given place in your code will always cause the compiler to=20
execute it at compile time then yes I could easily add a keyword (or some=20
other simple mechanism) that will do that. It would not be hard at all.

e.g.
 	int x =3D (execute now)fred();

I guess I could even add an attribute to the function itself so that it=20
only ever gets executed by the compiler, that would not be hard either.

Regards
Sergio Masci
--=20
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