On Wednesday, 16 October 2013 at 21:11:19 UTC, H. S. Teoh wrote:
On Wed, Oct 16, 2013 at 10:09:50PM +0200, Daniel Davidson wrote:
[...]
I reported my issue with the `chain` function to this NG and
tried
to start annotating items used by chain with pure to see how
far the
thread led. Honestly it was quickly clear that it led too far
for me
to follow it and someone else indicated the problem had to do
with
Voldermort types. If there is more I could do to "benefit us
all",
beyond learning how it works and what to avoid in my own code
- I
will be glad to try.
Hmm. I just did a quick-n-dirty change to Phobos, and it seems
to make
chain() usable with pure code. I'm not sure why the compiler
didn't
infer pure for it -- it should. (Or perhaps I'm missing
something
obvious -- I didn't run the Phobos unittest so maybe the
following
change breaks something.)
- In the Phobos source, edit std/range.d and look for the
function `auto
chain(Ranges...)(Ranges rs)` (around line 2022 or
thereabouts), then
the struct Result inside this function.
- Find the ctor for this struct (circa line 2074), and annotate
it with
pure.
- Now the following code compiles:
import std.range;
auto pureFunc() pure {
return chain([1,2,3], [2,3,4]);
}
void main() {
auto r = pureFunc();
}
This is just a hack, of course. The compiler *should* be able to
correctly infer that the ctor is pure. So the real fix is to
find out
why the compiler isn't doing that.
T
I am able to see your code work. However, when I make that change
and try to use chain in a pure function:
foreach(dateRate; chain(trisection[1], trisection[2])) {
Date earlyEnd = min(dateRate.when, end);
result = moveValueInTime(result, ccRate, currentDate,
earlyEnd);
ccRate = dateRate.value;
currentDate = earlyEnd;
if(earlyEnd == end) break;
}
I get: pure function 'plus.tvm.rate_curve.RateCurve.scaleFromTo'
cannot call impure function
'std.range.chain!(SortedRange!(const(TimePointValue!(Date,
CcRate))[], "a.when < b.when"),
SortedRange!(const(TimePointValue!(Date, CcRate))[], "a.when <
b.when")).chain.Result.empty'
So it seems more work is needed for real purity.
Thanks
Dan
