Our template emission strategy is broken

David Nadlinger via Digitalmars-d digitalmars-d at puremagic.com
Wed Nov 11 09:19:28 PST 2015

On Wednesday, 11 November 2015 at 15:04:01 UTC, Andrei 
Alexandrescu wrote:
> Yes, compiling package-at-a-time should be the mode endorsed by 
> the core community. Liran Zvibel and I discussed this privately 
> following his DConf 2015 talk, and I recall he mentioned the 
> package-at-a-time solved essentially all of their build 
> problems.

If you have a look at the bug report I linked in the original 
post, you'll find that this case occurs precisely with 
per-package compilation. Yes, there is a single cyclic 
inter-package dependency hidden somewhere deep inside the 
dependency graph, but getting rid of it after the fact would have 
either required re-structuring large parts of a ˜10^5 LOC code 
base, or would have again involved creating logical packages so 
large that the memory inefficiencies (CTFE is the biggest problem 
here) and run-time scaling issues (e.g. O(n^2) behavior in the 
overall number of templates) in the front-end become a problem 

Of course, many of the problems could have probably been avoided 
if there was an iron-clad rule that the module dependency graph 
must remain acyclic from the beginning of development (at least 
at the level of units of compilation). But how could they have 
known how bad it would get otherwise? I don't think this is 
reflected in our documentation anywhere, at least not in a 
prominent place.

  — David

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