On Sunday, 13 September 2020 at 18:24:01 UTC, mw wrote:
But, I'd reflect on my experience so far on compile-time
meta-programming in D as a novice user, the big problems are:
-- in D, there are too many choices, with no clear guideline
which one is *THE* one to use for a particular purpose:
language or library mechanisms? mixin? template? AliasSeq /
aliasSeqOf? Tuple? (non-)?-eponymous version of ...?; and even
for a particular option, e.g. Tuple!(int, "MA_optInTimePeriod",
TA_MAType, "opInMAType"), there are choices to use either
token (int) or string ("MA_optInTimePeriod"). And user does not
have a strong guide on which choice is *THE* way to proceed.
Each mechanism seems to have / fit a particular purpose, but
when you start to use it, you'll probably find there are new
problems come-in later, and you want to revisit the choice you
made earlier on.
By contrast, in C: there is only *ONE* mechanism, i.e. macro,
that's it.
I think the biggest issue here is that, like you said, it's hard
to find good resources for learning how to use D's various
reflection and code-generation facilities. In the community
Discord, we've tried to collect some links in the #resources
channel, which you might find helpful:
- Philippe Sigaud's "D Template Tutorial"
http://dpldocs.info/experimental-docs/std.typecons.Tuple.html
- Bradley Chatha's "Intro to D metaprogramming"
https://bradley.chatha.dev/Blog
- Vladimir Panteleev's "Functional Image Processing in D"
https://blog.thecybershadow.net/2014/03/21/functional-image-processing-in-d/
Ideally, we'd have some official, easy-to-find place where
tutorials like this could be collected (maybe on the Wiki?), but
so far no one's taken the initiative to set that up. One of the
downsides of having a volunteer community, I suppose.
-- in D, there is no easy way to convert between token <==>
string. Given a token, does token.stringof always work to paste
with other strings to generate a new token? and given a string,
does mixin!"string" always work to be a valid token?
There's no 100% reliable way to round-trip a token to a string
and back again, because the same token can have a different
meaning depending on what scope it's used in. Adam Ruppe goes
over some alternatives to string mixins you can use to avoid this
pitfall in one of his "Tips of the Week":
http://www.arsdnet.net/this-week-in-d/2016-feb-21.html
-- in D, there is no easy way to see directly the generated
source code by the compiler at compile-time, which makes the
debug difficult during development.
By contrast, in C: one can easily see the result via: cpp -P
foo.h > foo.c
I agree that this is an issue. There are a couple compiler flags
that can help (-mixin=filename, -vcg-ast), but mostly you're
stuck with printf-style debugging via `pragma(msg)`.
