* Win32 issues with Templates and Libs *

[Walter Bright]

Sean Kelly wrote:
> Let's back up for a second.  First, in the situation Kris mentioned, how 
> many instances of Test!(char) exist altogether?

One.

> I had expected there to 
> be two: one in test.lib and one in tester.obj.  But in this case I 
> wouldn't expect the link error to occur, so perhaps you're saying that 
> when the compiler sees "Test!(char) Global" in module test, it doesn't 
> bother to create one in tester.obj?

That's right.

> Also, how do COMDATs differ from normal code blocks?

COMDATs are each placed in their own segment.

> ie. Why is the 
> linker able to resolve normal symbols in libraries but not templates? 

Because normal symbols cannot appear multiple times (if they did, you 
get multiple definition errors at link time).

> Wouldn't the symbol name in both cases be enough to sort things out?

No.

> I guess this answers my question above: the compiler sees "Test!(char) 
> Global" and doesn't bother to create another instance of the code.  But 
> surely being able to create a functional application is preferable in 
> this case.  Won't an optimizing linker throw out duplicates anyway?

The problem is not knowing which module to link in - after all, there 
are (possibly) other global symbols in the module.

> Who 
> cares if the object files are bloated, if that's the only workable 
> option here?

You'll care <g> once templates get complex enough. It's been a big 
problem with C++.

> Or perhaps this suggests the need for a D linker that 
> builds a catalog of symbols inside libraries before linking instead of 
> the behavior you describe above?

Building a linker or object file with non-standard semantics has its own 
set of problems.