template instantiation question

[Ali Çehreli via Digitalmars-d-learn]

On 03/18/2015 11:03 AM, Dmitri Makarov wrote:

 > When these modules compiled separately, I assume, both a.o and b.o
 > contain a definition of i.c.S!void.S.transmogrify() instance.

That is very likely but I played with different three files for a while 
and failed to see that.

 > how is the symbol redefinition resolved when the three object
 > files are linked into a single executable?

There are different kinds of symbols. For example, the following command 
on a Linux console will show that template instances are weak symbols 
(it is not an error to have one or more weak symbols).

$ nm b.o | grep transmogrify
0000000000000000 W _D1c8__T1CTvZ1C12transmogrifyMFNaNbNiNfZi

'man nm' tells us that W indicates a weak symbol:

   "W"
   "w" The symbol is a weak symbol that has not been specifically
       tagged as a weak object symbol.  When a weak defined symbol is
       linked with a normal defined symbol, the normal defined symbol
       is used with no error.  When a weak undefined symbol is linked
       and the symbol is not defined, the value of the symbol is
       determined in a system-specific manner without error.  On some
       systems, uppercase indicates that a default value has been
       specified.

Ali