On 1/27/14 10:40 AM, Pierre Talbot wrote:
On Monday, 27 January 2014 at 01:39:47 UTC, Simen Kjærås wrote:
On 2014-01-26 09:59, Pierre Talbot wrote:> Hi,
>
> I was wondering why CTFE is context sensitive, why don't we
check
> every expressions and run the CTFE if it applies?
Mostly because it's not necessary, and takes more time than simply compiling
it. For an
optimization step, opportunistic CTFE would certainly be possible (it is, after
all, simply
constant folding on steroids).
The situations in which CTFE is attempted today are when it's explicitly
required - either because
the value is used at compile time, or because it's assigned to a manifest
constant or static
variable (which are defined to be required to be known at compile time).
This means the compiler does not need to spend inordinate amounts of time
testing to see if the
code compiles with CTFE, and that it can give sensible error messages when
something cannot be
CTFE'd. If instead opportunistic CTFE were the norm, you would need to
disassemble your program to
see if the compiler did in fact CTFE the code that you think it should.
--
Simen
We could do opportunistic CTFE by default, and if the user want to ensure it is
done, instead of
disassemble the program, he could just use the usual techniques (static, ...).
But ok, what I wanted to hear is that it is theoretically possible but
technically problematic.
Thanks to all,
Pierre
One of the problems is on the opposite side, ensuring it's NOT done when you don't want it to be.
Consider an example where you have a blob of obfuscated data and a de-obfuscation routine. It
_could_ be executed at compile time, but that defeats the point. What we have right now puts the
control in the hands of the developer.
