beginner's linking error

[James Cranch]

Hi all,

I've just installed gdc from Debian Stable (gdc (Debian 
6.3.0-18+deb9u1) 6.3.0 20170516), and have been having linker 
errors when using writeln.

A minimal nonworking example is as follows: I have a file 
library.d which contains the following:

| module library;
|
| import std.stdio;
|
| class Greeter(string s) {
|
|   this() { }
|
|   void say_hello() {
|     writeln("Hello ", s, "!");
|   }
| }

I also have a file executable.d which contains the following:

| module executable;
| import library;
|
| int main() {
|
|   alias G = Greeter!("James");
|   G a = new G();
|   a.say_hello();
|   return 0;
| }

An attempt to compile it looks as follows:

| $ gdc executable.d -o executable
| /tmp/cc4RjTlb.o:(.data.rel+0x10): undefined reference to 
`_D7library12__ModuleInfoZ'
| collect2: error: ld returned 1 exit status

If I remove the import std.stdio and the writeln command from 
library.d, then it all works, so I'm clearly not linking 
libraries right, but it's not clear to me what to do.