Weird link error

[CodeSun via Digitalmars-d-learn]

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.

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?

And where I can find the D symbol definition, because information 
like ‘_D2tt2Ti12__T3getTAyaZ3getMFAyaZAya’ makes me really 
confused.