Migrating dmd to D?

[Walter Bright]

On 2/27/2013 4:57 PM, H. S. Teoh wrote:
> How will this work with the continual stream of fixes that the current
> C++-based compiler is getting? I assume we're not just going to put DMD
> development on hold.

I've done many projects consisting of converting a medium sized code base from 
one language to another. The way that works is to do it incrementally. 
Incrementally means:

1. at each step (i.e. pull request) we will have a fully functioning D compiler 
that passes its test suite

2. there is no divergence in code bases because there is not a divergent code base.

> Also, wouldn't this be a good time to review some of the current designs
> in DMD that may be hampering the full implementation of features that
> we'd like, such as discrepancies with TDPL, etc.? Would it make sense to
> redesign some of the code currently causing hard-to-fix issues as we're
> porting that part of DMD into D? It seems a bit counterproductive to
> simply transcribe the current buggy code into D, only to rewrite it
> later when (if) we finally get round to fixing it.

My experience chiming in - never ever ever attempt to refactor while 
translating. What always happens is you wind up with a mess that just doesn't work.


> Finally, I think somebody has brought up the idea of "freezing" a
> particular subset of D that the D compiler can use in its own code,
> preferably a reasonably simple subset that is safe from breaking changes
> down the road (it would be pathetic if a breaking change causes the
> compiler to be unable to compile itself, because the source code uses a
> language construct that was later deemed to need redesign). As DMD is
> ported over to D, it should be restricted to using only this subset of
> the language, so that it does not hamper future developments of the
> language unnecessarily.

Experience chiming in - a successful model is that the HEAD is compiled by the 
previous official release of D.