There are quite a few fallacies in there.
On Monday, 2 January 2017 at 21:23:19 UTC, Andrei Alexandrescu
wrote:
Regarding the ongoing doubts about the advantages of inline
imports: they are first and foremost a completion of the nested
import feature. As such, most, if not all, arguments against
inline imports apply equally to nested imports. Come to think
of it, lazy imports vs nested imports:
* same improvement in compilation speed? check
* no language changes? check
* no nasty bugs in the aftermath (such as the infamous
https://issues.dlang.org/show_bug.cgi?id=10378)? check
* scalable builds? check
Yet local imports are overwhelmingly superior to lazy imports
because of one thing: they localize dependencies. They
introduce modularity and its ancillary perks (fast and scalable
builds, easier review and refactoring) not by engineering, but
by organically placing dependencies spatially with their
dependents. (The scope statement does the same thing with
temporal dependencies.) That the DIP does not make it clear
that it is a necessary and sufficient extension of local
imports is a problem with it.
There is a major difference with this DIP.
Lazy import is not a language change, but a compiler
implementation detail. As such, it doesn't require a DIP or
anything specific.
Nested import are a language simplification. Declaration can
appear anywhere, import is a declaration, the fact that import
couldn't appear anywhere was an arbitrary limitation, and
removing it makes the language simpler. As such, the burden of
proof is on maintaining the limitation rather than removing it.
This DIP is a language addition. Therefore, contrary to nested or
lazy import, the burden of proof is on it. This DIP should be
considered as follow: how much complexity does it add and how
much benefit does it bring, compared to alternatives.
The obvious benefit is localizing dependencies. I think I'm not
too far off track by considering most of the speedup and scalable
build can be achieved with lazy import and, while I'm sure there
are example where this is superior, we are talking marginal gains
as lazy and nested imports squeezed most of the juice already.
The cost is the language addition. The first obvious improvement
that can be made to this DIP to reduce its cost is to not
introduce a new syntax. As such, the addition is limited to
allowing the existing syntax in a new place rather than adding a
whole new syntax for imports.
I like the extra expressivity. I'm not 100% convinced it is worth
the extra cost, but the more the cost is reduced, the more
rational it seems to me that this option should be pursued.
I now am really glad we slipped local imports before the
formalization of DIPs. The feature could have been easily
demeaned out of existence.
Good you also notice how broken the DIP process is.
One suggestion: let's keep the DIP describing the change to be
made. Some examples are fine to illustrate, but it is not the
DIp's purpose to be easy to understand or expand too much in
argumentation, or it'll be useless as a spec document, and trying
to have the DIP be a spec, a tutorial, a essay on why the
feature, and so on just lead to endless rewriting lead to
perpetual motion but no progress.
