On Tuesday, 8 March 2016 at 11:50:32 UTC, Peter wrote:
Hi,
Can anyone explain to me what's causing the following code to
generate a missing symbol error...
import std.stdio;
interface IProblem {
void writeln(T...)(T arguments);
}
class Problem : IProblem {
void writeln(T...)(T arguments) {
// This is just here to have code in an implementation.
stdout.writeln("The implementation function was called.");
}
}
IProblem getProblem() {
return(new Problem());
}
void main() {
auto problem = getProblem();
problem.writeln("Some text and a number - ", 1234);
}
Now obviously this codes a bit contrived but its my attempt to
reduce an issue I'm seeing to its more concise form. Note that
if I cast the return value from the call to getProblem() to a
Problem instance this rectifies the issue but I'm unclear as to
why this might be. The error I get when I compile this is...
Undefined symbols for architecture x86_64:
"_D3app8IProblem18__T7writelnTAyaTiZ7writelnMFAyaiZv",
referenced from:
__Dmain in template_issue.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v
to see invocation)
--- errorlevel 1
dmd failed with exit code 1.
Apologies is the cause is blatantly obvious to more experienced
D coders.
Regards,
Peter
Probably because the idea of a template function in an interface
is
wrong, and I'm surprised that dmd accepts that. The reason is that
declaring a (non final)template function in an interface is like
declaring a
function pointer to an uninstansiated(sp?) template function. Also
how many copies should appear in the vtbl for different template
argument combinations?
Calling a templates on a class is fine, which explains why
casting
solves the issue.
Solutions: if the function in the interface must take template
args
parameterise the interface not the function (not sure if this
works)
OR
if the function must take a variable number of args just use
regular
runtime varadic arguments.
Nic
