I am getting linker errors with this stripped-down example:

my_main.d:

import std.stdio;
import std.complex;
import my_module;

void main(){
      my_TYPE xxx;
      writeln(xxx);
}

my_module.d:

module my_module;

import std.complex;

alias my_TYPE = Complex!double; // this causes link error: "undefined reference"

/* alias my_TYPE = double; */ // this works fine

Why does the linker fail when I alias to the Complex!double ...
but would work fine when alias to the double ??

Any help to understand what is greatly appreciated.
James

On Tuesday, 3 August 2021 at 21:40:09 UTC, james.p.leblanc wrote:

void main(){
      my_TYPE xxx;
      writeln(xxx);
}

The alias to Complex!double is a template instantiation. A template instantiation creates a symbol that needs to be linked. So you need to compile my_module.d along with my_main.d.

dmd my_main.d my_module.d

Or alternatively:

dmd -i my_main.d

double is a built-in type, so that alias doesn't create any symbols that need linking.

An alias in and of itself is a compile-time-only construct, but the symbols you assign it might require linking something.

On Wednesday, 4 August 2021 at 01:10:15 UTC, Mike Parker wrote:

dmd my_main.d my_module.d

dmd -i my_main.d

Mike,

Aha... that makes sense now!

Thanks kindly for helping me understand what was happening with your
informative reply. The fact of template instantiations and symbols
had escaped me completely.

I appreciate it.

Best Regards,
James