• JN (17/17) Sep 20 2019 import std.stdio;
• Adam D. Ruppe (3/5) Sep 20 2019 because you never used it. templates don't get checked by the
• =?UTF-8?Q?Ali_=c3=87ehreli?= (18/36) Sep 20 2019 No. Function templates cannot be virtual functions. There are at least

JN <666total wp.pl> writes:

import std.stdio;

interface IWriter
{
     void write(U)(U x);
}

class Foo : IWriter
{
     void write(U)(U x, int y)
     {
         writeln(x);
     }
}



void main()
{
}

Does this code make sense? If so, why doesn't it throw an error 
about unimplemented write (or incorrectly implemented) method?

Adam D. Ruppe <destructionator gmail.com> writes:

On Friday, 20 September 2019 at 19:02:11 UTC, JN wrote:
 If so, why doesn't it throw an error about unimplemented write 
 (or incorrectly implemented) method?

because you never used it. templates don't get checked by the 
compiler until they are used...

=?UTF-8?Q?Ali_=c3=87ehreli?= <acehreli yahoo.com> writes:

On 09/20/2019 12:02 PM, JN wrote:
 import std.stdio;

 interface IWriter
 {
      void write(U)(U x);
 }

 class Foo : IWriter
 {
      void write(U)(U x, int y)
      {
          writeln(x);
      }
 }



 void main()
 {
 }

 Does this code make sense?

No. Function templates cannot be virtual functions. There are at least 
two reasons that I can think of:

1) Function templates are not functions but their templates; only their 
instances would be functions

2) Related to that, languages like D that use virtual function pointer 
tables for dynamic dispatch cannot know how large that table should be; 
so, they cannot compile for an infinite number of entries in that table

 If so, why doesn't it throw an error about
 unimplemented write (or incorrectly implemented) method?

Foo.write hides IWriter.write (see "name hiding"). Name hiding is not an 
error.

When you call write on the Foo interface it takes two parameters:

   auto i = new Foo();
   i.write(1, 2);    // Compiles

When you call write on the IWriter interface it takes one parameter but 
there is no definition for it so you get a linker error:

   IWriter i = new Foo();
   i.write(1);    // LINKER ERROR

Ali