forcing compile time function execution

[Vladimir Panteleev]

On Tuesday, 27 December 2011 at 20:11:32 UTC, Joshua Reusch wrote:
> Am 27.12.2011 20:51, schrieb Vladimir Panteleev:
>> On Tuesday, 27 December 2011 at 19:46:31 UTC, Joshua Reusch 
>> wrote:
>>> Am 27.12.2011 20:35, Vladimir Panteleev wrote:
>>>> Halting problem?
>>>
>>> Makes an not-stopping pure function really sense?
>>
>> No, but you don't know if the user is expecting the function 
>> to take a
>> long time to run, or it's stuck due to a bug.
>>
>
> If the function gets evaluated at compile-time, also the 
> loop/recursion conditions are known.

We're back at the halting problem. There are heuristics, but you 
can't know for sure.

For example:

for (auto i=arr.length-1; i>=0; i--)

On 64-bits, i will be 64 bits too (because arr.length is size_t). 
Since it's unsigned, the loop will wrap, and it'll take a very 
long time until it'll reach a state it's been in before.