Missing introspection? "How exactly this type is actually used"

[Ali Çehreli]

On 5/20/22 11:04, Adam D Ruppe wrote:
 > On Friday, 20 May 2022 at 17:45:01 UTC, Ali Çehreli wrote:
 >> What if the user never uses those costly members of that particular
 >> instantiation?
 >
 > If the functions themselves are templates, if they are never used, it
 > will never be instantiated. That's a way you can do this kind of thing.

Interesting. That sounds like a general guideline to all user-defined types.

I think the cost would be multiple compilations of those member function 
instances, N-1 of which could be eliminated by the linker.

The issue with the member variables remains: Currently, there is no way 
of determining that a member variable is used only by a set of member 
function instances that are never generated, meaning that the member 
variable could be eliminated. (For this, we are clearly talking about 
struct and class templates.) But as I understand, the compiler cannot 
see through function interfaces to determine what exactly is used on the 
other side. So we would end up with mismatched types.

Ali