Weird template instantiation speed?

[IchorDev]

On Sunday, 9 July 2023 at 14:49:39 UTC, Steven Schveighoffer 
wrote:
>
> This is probably a bug somewhere, 4 seconds is too much. A 
> reduced test case would be helpful.
>
> But I wanted to note, inside a struct template, the template 
> name (by itself) is equivalent to the current instantiation. So 
> just returning `BindingTempl` would be equivalent, and might 
> not trigger this problem.
>
> See if that helps.
>
> -Steve

Thank you for letting me know about being able to use 
`BindingTempl`, I had no idea! Unfortunately it doesn't mitigate 
the compile times, though.
I forgot to mention, it only happens when specifying `-O` with 
DMD. LDC and GDC compile the same thing almost instantly.
Boiling it down to a simple test is tough. If you remove a lot of 
components the struct template depends on then the compile time 
is too fast for anything to be noticeable. I think the issue is 
some kind of snowball-effect.

If anyone wants to try to reproduce this issue:
1. Download [this exact 
commit](https://github.com/ichordev/bindbc-imgui/tree/65d02d68e4188250c948147a04a5820de3479a44) of the WIP BindBC-ImGui repo. (the newer commits won't compile)
2. Edit dub.selections.json to change `"bindbc-common"`'s version 
to `"0.0.6"`.
3. Run:
```
dmd -extern-std=c++11 -lib -O -version=BindImGui_Static -Isource/ 
-I~/.dub/packages/bindbc-common/0.0.6/bindbc-common/source/ 
source/bindbc/imgui/config.d source/bindbc/imgui/package.d 
source/imgui/impl.d source/imgui/package.d -v
```

4. Now, remove `-O` from the dmd command. Blink and you'll miss 
it compiling!