Re: Missing Symbol Accessing Templated Function Through Interface

[Peter via Digitalmars-d-learn]

On Tuesday, 8 March 2016 at 12:24:06 UTC, crimaniak wrote:

On Tuesday, 8 March 2016 at 11:50:32 UTC, Peter wrote:

Hi,

Can anyone explain to me what's causing the following code to 
generate a missing symbol error...


Relevant comment: 
https://issues.dlang.org/show_bug.cgi?id=8553#c1


Thanks for link, makes sense.

Re: Missing Symbol Accessing Templated Function Through Interface

[crimaniak via Digitalmars-d-learn]

On Tuesday, 8 March 2016 at 11:50:32 UTC, Peter wrote:

Hi,

Can anyone explain to me what's causing the following code to 
generate a missing symbol error...


Relevant comment: https://issues.dlang.org/show_bug.cgi?id=8553#c1

Re: Missing Symbol Accessing Templated Function Through Interface

[Nicholas Wilson via Digitalmars-d-learn]

On Tuesday, 8 March 2016 at 11:50:32 UTC, Peter wrote:

Hi,

Can anyone explain to me what's causing the following code to 
generate a missing symbol error...


import std.stdio;

interface IProblem {
   void writeln(T...)(T arguments);
}

class Problem : IProblem {
   void writeln(T...)(T arguments) {
  // This is just here to have code in an implementation.
  stdout.writeln("The implementation function was called.");
   }
}

IProblem getProblem() {
   return(new Problem());
}

void main() {
   auto problem = getProblem();

   problem.writeln("Some text and a number - ", 1234);
}

Now obviously this codes a bit contrived but its my attempt to 
reduce an issue I'm seeing to its more concise form. Note that 
if I cast the return value from the call to getProblem() to a 
Problem instance this rectifies the issue but I'm unclear as to 
why this might be. The error I get when I compile this is...


   Undefined symbols for architecture x86_64:
 "_D3app8IProblem18__T7writelnTAyaTiZ7writelnMFAyaiZv", 
referenced from:

 __Dmain in template_issue.o
   ld: symbol(s) not found for architecture x86_64
   clang: error: linker command failed with exit code 1 (use -v 
to see invocation)

   --- errorlevel 1
   dmd failed with exit code 1.

Apologies is the cause is blatantly obvious to more experienced 
D coders.


Regards,

Peter


Probably because the idea of a template function in an interface 
is

wrong, and I'm surprised that dmd accepts that. The reason is that
declaring a (non final)template function in an interface is like 
declaring a

function pointer to an uninstansiated(sp?) template function. Also
how many copies should appear in the vtbl for different template
argument combinations?
 Calling a templates on a class is fine, which explains why 
casting

solves the issue.

Solutions: if the function in the interface must take template 
args
parameterise the interface not the function (not sure if this 
works)

OR
if the function must take a variable number of args just use 
regular

runtime varadic arguments.

Nic

Missing Symbol Accessing Templated Function Through Interface

[Peter via Digitalmars-d-learn]

Hi,

Can anyone explain to me what's causing the following code to 
generate a missing symbol error...


import std.stdio;

interface IProblem {
   void writeln(T...)(T arguments);
}

class Problem : IProblem {
   void writeln(T...)(T arguments) {
  // This is just here to have code in an implementation.
  stdout.writeln("The implementation function was called.");
   }
}

IProblem getProblem() {
   return(new Problem());
}

void main() {
   auto problem = getProblem();

   problem.writeln("Some text and a number - ", 1234);
}

Now obviously this codes a bit contrived but its my attempt to 
reduce an issue I'm seeing to its more concise form. Note that if 
I cast the return value from the call to getProblem() to a 
Problem instance this rectifies the issue but I'm unclear as to 
why this might be. The error I get when I compile this is...


   Undefined symbols for architecture x86_64:
 "_D3app8IProblem18__T7writelnTAyaTiZ7writelnMFAyaiZv", 
referenced from:

 __Dmain in template_issue.o
   ld: symbol(s) not found for architecture x86_64
   clang: error: linker command failed with exit code 1 (use -v 
to see invocation)

   --- errorlevel 1
   dmd failed with exit code 1.

Apologies is the cause is blatantly obvious to more experienced D 
coders.


Regards,

Peter