On Monday, 20 April 2015 at 17:02:18 UTC, CodeSun wrote:
I have test a snippet of code, and I encountered with a weird
link error.
The following is the demo:
import std.stdio;
interface Ti {
T get(T)(int num);
T get(T)(string str);
}
class Test : Ti {
T get(T)(int num) {
writeln("ok");
}
T get(T)(string str) {
writeln(str);
}
}
void main() {
Ti tt = new Test;
tt.get!string("test");
tt.get!string(123);
}
When I use dmd to compile this code snippet, the following link
error was reported:
tt.d:(.text._Dmain+0x3b)：‘_D2tt2Ti12__T3getTAyaZ3getMFAyaZAya’
undefined reference
tt.d:(.text._Dmain+0x49)：‘_D2tt2Ti12__T3getTAyaZ3getMFiZAya’undefined
reference
And if I modigy the code to
Test tt = new Test;
then this code will work.
Template methods are non-virtual. That is, you can't override
them.
So does it mean I can't declare function template inside
interface? If so, why didn't dmd report the error while
compiling instead of linking?
You can theoretically implement them elsewhere. For example, this
works:
module test;
interface Ti {
T get(T)(int num);
T get(T)(string str);
}
pragma(mangle, "_D4test2Ti12__T3getTAyaZ3getMFiZAya") string
impl(int)
{
return "foo";
}
pragma(mangle, "_D4test2Ti12__T3getTAyaZ3getMFAyaZAya") string
impl(string)
{
return "bar";
}
class Test : Ti {}
void main() {
Ti tt = new Test;
tt.get!string("test");
tt.get!string(123);
}
It's really silly, though. I don't know if there's a more
realistic use case.
And where I can find the D symbol definition, because
information like ‘_D2tt2Ti12__T3getTAyaZ3getMFAyaZAya’ makes me
really confused.
That's a mangled name. There's a tool called ddemangle. It comes
with the D releases. You can pipe the compiler output through it
to get more readable symbol names (don't forget to redirect
stderr to stdout). For this one it gives gives you
"immutable(char)[]
tt.Ti.get!(immutable(char)[]).get(immutable(char)[])".
