• james.p.leblanc (22/22) Aug 03 2021 I am getting linker errors with this stripped-down example:
• Mike Parker (15/37) Aug 03 2021 The alias to Complex!double is a template instantiation. A
• james.p.leblanc (11/28) Aug 03 2021 Mike,

james.p.leblanc <james.p.leblanc gmail.com> writes:

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

Mike Parker <aldacron gmail.com> writes:

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

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.

james.p.leblanc <james.p.leblanc gmail.com> writes:

On Wednesday, 4 August 2021 at 01:10:15 UTC, Mike Parker wrote:
 On Tuesday, 3 August 2021 at 21:40:09 UTC, james.p.leblanc 
 wrote:
 [...]

 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.

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