[Development] better compile-time os detection

[Thiago Macieira]

On Thursday, 23 July 2026 19:20:41 Pacific Daylight Time EXT Tim Blechmann via 
Development wrote:
> depending on the code, one could utilize tag dispatching, so only then
> overload declarations would require the preprocessor.
> ```
> #ifdef LINUX
> auto rename(auto src, auto target, Os::LinuxT) {
>      return renameat2(...);
> }
> #elif DARWIN
> auto rename(auto src, auto target, Os::DarwinT) {
>      return renameatx_np(...);
> }
> #endif
> 
> auto rename(auto src, auto target)
> {
>      return rename(src, target, Os::Current); // no ifdef
> }
> ```

Why would you do that? What's the advantage? If you remove the tag, it would 
compile to the same thing.

> it is mainly useful for cases where no platform-specific APIs are
> involved, but one still wants to do per-platform decisions.

Right, things like "does this platform use .so suffix or .dylib?" Those aren't 
detections, they are defaults we apply.

-- 
Thiago Macieira - thiago.macieira (AT) intel.com
  Principal Engineer - Intel DCG - Platform & Sys. Eng.
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