"Jonathan M Davis" <[email protected]> wrote in message
news:[email protected]...
On Wednesday 21 July 2010 00:09:05 Don wrote:
While running the semantic on each function body, the compiler could
fairly easily check to see if the function is CTFEable. (The main
complication is that it has to guess about how many iterations are
performed in loops). Then, when a CTFEable function is called with
compile-time constants as arguments, it could run CTFE on it, even if it
is not mandatory.
Incidentally, having the function being marked as 'pure' doesn't really
help at all for determining if it is CTFEable.
Hmm. As I understood it, it did.
You understood right.
But I guess that if it did, the compiler could
technically determine whether a function was actually pure anyway by
looking at
its body. All the pure attribute would do is save it the trouble. So, the
pure
attribute wouldn't do much in that sense except save the compiler some
computation.
pure functions must halt, so the attribute let's you tell the compiler
something that it could only figure out with difficulty, if at all.
I can certainly see why being pure wouldn't be enough to be CTFEable
(since pure
doesn't guarantee anything about whether it's parameters are know at
compile
time), but I would have thought that the lack of global state would be
required
- at least the lack of global state which isn't known at compile time -
for it
to be CTFEable, in which case the pureness would help.
In any case, I'd obviously have to study it up a bit more to understand
exactly
what's required for CTFEability. I have some idea, but obviously not
enough.
- Jonathan M Davis
