On Friday, 6 September 2019 at 00:41:12 UTC, Jonathan M Davis
wrote:
On Thursday, September 5, 2019 6:24:07 PM MDT Jamie via
Digitalmars-d-learn wrote:
/home/jamie/.dvm/compilers/dmd-2.077.0/linux/bin/../../src/phobos/std/math
.d(3702): Error: fmodl cannot be interpreted at compile time,
because it
has no available source code called from here: called from
here:
fmod(cast(real)to(n),
cast(real)to(2))
Thanks
Based on that implementation, fmod would work at compile time
if you compile on Windows and use Microsoft's runtime instead
of Digital Mars runtime (so, if it was compiled as 64-bit or it
used whatever the flag is to force the COFF format instead of
OMF for 32-bit). It won't work on any other platform at compile
time, because core.stdc.math.fmodl is a C function, and C
functions cannot be called at compile time.
By any chance were you compiling this on Windows previously
rather than Linux? If so, that's likely why the code worked
before and doesn't now. If you were always compiling on Linux,
then I don't know why you were able to compile your code
before. A quick glance at the repo history shows that fmod has
had that same implementation since 2012, so there should be no
way that it was callable on any Linux system even 6 years ago,
let alone 6 months ago.
- Jonathan M Davis
Thanks for the reply. I haven't used Windows in the past two
years so that isn't the issue in my case. After your comments I
looked deeper, and I think my issue is related to compile time
values, and me misunderstanding default arguments for structs.
import std.stdio;
import std.conv: to;
import std.math: fmod;
void main()
{
/// without default arguments
S s = S(64, 64); // case 1: works
// static S s = S(64, 64); // case 2: doesn't work
/// with default arguments
// static S s = S(); // case 3: works
}
struct S
{
this(size_t N, size_t M) {
// this(size_t N=64, size_t M=64) {
f(N, M);
}
}
void f(size_t N, size_t M)
{
int kj(int n)
{
return to!int(fmod(n, 2));
}
int k = kj(2);
}
If I'm understanding it correctly now, in case 1 the struct
constructor isn't called at compile time, so the underlying C
function (fmod) is not called. In case 2 because the struct is
called in a static region, the constructor is called at compile
time and fmod is called so it breaks. In case 3, with default
struct arguments, I thought that the constructor I have defined
was being called, however the default constructor was being
called (this()) so fmod wasn't being called.
The reason why my old code worked was because it used the default
arguments and I wasn't actually calling the constructor I
defined. When I removed the default arguments in the constructor
and tried case 2 it obviously didn't work.
Am I understanding correctly? Thanks
