Solutions to the TypeInfo dependency injection issue?

[Sean Kelly]

kris wrote:
> Walter Bright wrote:
>> kris wrote:
>>
>>> Walter Bright wrote:
>>>
>>>> kris wrote:
>>>>
>>>>> What about (c) how templates are affected at each step ?
>>>>
>>>>
>>>>
>>>> It's the same algorithm - nothing special about templates.
>>>
>>>
>>> Is it possible, do you think, to be just a little more forthcoming on 
>>> this?
>>>
>>> 1) when you batch-compile code with multiple references to a 
>>> template, there is just one instance generated.
>>
>>
>> Yes.
>>
>>> 2) when you compile the same code modules individually, there are 
>>> presumably multiple template instances generated?
>>
>>
>> Yes.
>>
>>> 3) how does the linker resolve the multiple template instances to 
>>> just one?
>>
>>
>> The template instantiations are put into COMDAT sections, and the 
>> linker discards redundant ones.
> 
> Thank you;
> 
> 4) all symbols required to represent typeinfo and templates are now 
> duplicated in each object file ?

My guess is separate compilation generates all TypeInfo and templates 
used by that module into the module's object file.  Which I believe is a 
"yes."

> 5) The linker does not have to search beyond the current object file for 
> instances of #4 (as suggested by larsivi) ?

Correct.

> 6) the result is a library with many more duplicate symbols than before, 
> but arranged in such a manner that persuades the linker to do the "right 
> thing" ?

Yes.

> 7) there is no possibility of the linker following a 'bad chain', and 
> thus linking in unused or otherwise redundant code ?

It certainly seems that way.  We get larger object files and libraries 
in exchange for smaller executables.  If any of the above is wrong, 
someone please correct me.


Sean