Speeding up importing Phobos files

[Vladimir Panteleev]

On Monday, 21 January 2019 at 19:01:57 UTC, Steven Schveighoffer 
wrote:
> I still find it difficult to believe that calling exists x4 is 
> a huge culprit. But certainly, caching a directory structure is 
> going to be more efficient than reading it every time.

For large directories, opendir+readdir, especially with stat, is 
much slower than open/access. Most filesystems already use a hash 
table or equivalent, so looking up a known file name is faster 
because it's a hash table lookup.

This whole endeavor generally seems like poorly reimplementing 
what the OS should already be doing.