On Monday, 19 February 2018 at 15:58:57 UTC, Joakim wrote:
17. Allow multiple selective imports from different modules in
a single import statement
Let me hopefully conclude this discussion :).
We have an existing ambiguity in the language since at least dmd
1.0. This is unfortunate but seems costly to remove and minor in
impact (after learning this behavior).
import trees, fruits : apple, birds;
A newcomer to D could rightfully conclude that comma is a module
separator and the following is the correct syntax to import
multiple symbols.
import std.stdio, std.conv : to, std.conv : parse;
Embracing that existing ambiguity to support multi-module
selective imports wasn't well received, partly because it
amplifies the ambiguity and partly because multi-module imports
are frowned upon.
On the plus side, we've understood that the actual wish for that
syntax arised from scripting and example contexts, which might be
better addressed by
https://dlang.org/changelog/2.079.0.html#std-experimental-scripting, lazy import resolution by the compiler or a library, or automatic imports (https://github.com/CyberShadow/AutoFix).
Furthermore there remain various ideas that would avoid the
original ambiguity. Whether such changes are worthwhile is up for
discussion and would benefit from someone taking the lead.
I still think that local imports are nice for being explicit and
toolable but have the downside of being brittle.
Something like bash style expansion could help to hit a sweet
spot IMHO.
import std.{algorithm : {find, findSplit}, stdio : writeln};
import std.experimental.allocator.building_blocks.{free_list,
region};
But certainly anything in that direction requires time and
research, which I don't have for that topic.
In hindsight the voting experiment on
https://github.com/dlang/dmd/pull/6589 might have prevented
useful early feedback and thinking.
Given the effort required for a language change, it's seductive
to streamline seemingly small changes, but it certainly increases
the risk of design mistakes, thanks for appealing against this
one.
-Martin
