I've been learning D for a few weeks now.
I'm an experienced programmer in other languages (esp. Python,
but also Rust and C++).
Here're some *early* impressions and notes.
D Tour
I found the D Tour, esp. "D's Basics" to be very helpful. Each
part is short and in most cases understandable. Being able to run
and edit the code is a real help for learning.
D Playground
The D playground https://run.dlang.io/ is very useful for trying
out snippets and generally learning, so I use it a lot. (I still
haven't worked out how to save a URL to my code though.)
Library Reference Documentation
The Library Reference documentation seems to be a mixed bag.
Often I've found a good overview at the start, but then few or no
examples in the docs for classes and methods (see e.g.,
https://dlang.org/phobos/std_zip.html#.ZipArchive).
I don't find the presentation of the member properties and
methods very easy to read, but the worst aspect is the lack of
examples.
Standard Library
The library itself "feels" a bit incomplete, which is surprising
given how long D's been around. To give just two examples:
The lack of set and B-tree types is disappointing (esp.
considering that the much younger Rust has them). I'm using
rbtree for sets but that imposes a requirement that my items
support < (rather than the == or hash I'd expect for a set).
The fact that the return value of std.file.getAttributes() means
completely different things on POSIX and Windows. That's fair
enough, but there ought to be a platform-neutral equivalent for
those writing cross-platform applications that returned, say, a
struct or tuple with the common subset of attributes normalised.
(And if there is such a function, why isn't it cross-referenced.)
There seems to be a curious mixture of functions which are POSIX-
or Windows-specific and those which are platform neutral.
The D Language
The D language seems to be a "kitchen sink" (i.e., has
everything) like C++, Rust, (and nowadays, Python). This makes it
big and a *lot* to learn. However, I managed to create a little
library that used template types (with some help from this
forum), and I _understand_ the templates. This is a huge
improvement over C++ or Rust. And to my surprise, so far my D
programs have about the same line counts as the Python versions.
Also, I've found building much easier than C++. However, dub
doesn't seem to be competitive with Rust's cargo. Getting fast
statically built (no dependency) executables is really nice.
GUI Programming
I've tried a number of D GUI libraries, and all bar one have been
problematic.
To my surprise GtkD was easy to install on both Linux and Windows
and getting "hello world" to build and run was fairly easy. The
documentation doesn't seem that easy to use, but I'll start with
Ron Tarrant's https://gtkdcoding.com/ and see how I get on from
there.
D Books
I find Ali Çehreli's book (http://ddili.org/ders/d.en/index.html)
more suited to complete beginners, but I am skim reading it and
finding it useful here and there.
The main books I'm reading are Mike Parker's Learning D and Adam
Ruppe's D Cookbook, both of which I think are pretty good.
(However, I hope both will produce more up-to-date and improved
second editions with a better publisher.)
Learn D Forum
People on this forum have always provided polite and helpful
answers. This is a very important intangible benefit of the
language.
Conclusion
My hope was that D would offer a sweet spot between Python's ease
and speed of development and Rust's performance. And so far this
looks like being the case.
