I just wanted to share some experience of using D in industry.
Recently my little company released version 2.0 of our flagship
product Video Enhancer, a video processing application for
Windows, and this time it's written in D.
Couple of screenshots:
Version 1 was born like 10 years ago and was of course written in
C++. It consisted of main GUI executable and 5 dynamically loaded
DirectShow filters. For GUI version 1 used MFC and a third-party
skinning engine. This skinning engine had its own problems but
since we didn't have its sources we couldn't fix them, meanwhile
its author disappeared in sands of time. So when time has come to
create version 2 I chose the best available language and an open
source GUI library with 100% control and customizability -
DLangUI. Overall, I'm pretty happy with this choice.
Version 2 is quite different from v1 in feature set and internal
structure, it's not a direct translation. It consists of two
executables running in tandem (one does GUI, the other deals with
video) and 2 dynamically loaded DirectShow filters. Both main
executables are purely in D, while the DirectShow filters are
still in C++. Heavy number crunching, including our main feature
- motion-based video upscaler - is still in C++, because of heavy
SIMD usage and Intel compiler.
Main executable of version 1 was ~34K lines of C++ (half of which
were libraries like pugixml) and full build took ~90 seconds.
Main executables of version 2 are in total ~7.5K lines of D (of
which 2K are auto generated by IDL2D tool) and full build of GUI
app takes 7 seconds (and the worker app builds in 3-4 seconds),
so that's a really nice improvement.
Thanks to Phobos we don't need many libraries: things like XML
parsing, ZIP unpacking and many others are all covered by the
standard library. Only two additional libraries were used:
Cerealed for serialization of messages the two processes
exchange, and DLangUI.
Some things to reflect on:
Compiler used is DMD 2.070, 32-bit target. Video Enhancer
supports 200+ plugins from VirtualDub and they happen to be
32-bit, so our app has to be 32-bit too. Speed of code generated
by DMD is more than enough, even debug builds were fast enough.
The default linker is used (not the MS one), and I was worried
there might be some troubles with antivirus false positives (that
happened before when using optlink) but no, everything went
smooth and no problems with optlink arose whatsoever.
Visual Studio 2010 with VisualD. I've used this combo for many
years, generally quite successively. Last year its D parser had
some problems that made it crash on code that used DLangUI, and
that was painful. I even made a patch that made the crash silent,
so VisualD would silently reload the parser and continue working.
It worked, but luckily authors of D parser and VisualD quickly
found the crash cause and fixed it, since then everything works
smoothly out of the box. I like how well DML works there, with
syntax highlighting and autocompletion:
We're not using Dub to build the app, it tends to be slow and
rebuild dependencies too often (or maybe I just haven't learnt to
use it properly). Instead we use Dub to build the libraries and
produce .lib files, then reference libraries sources and lib
files in VisualD project of the main apps and then use VisualD's
simple building process that just invokes DMD.
This compile-time-introspection-based serializaition lib is
really great: powerful and easy to use. We're probably using an
old version, haven't updated for some time, and the version we
use sometimes had problems serializing certain types (like
bool, IIRC), so sometimes we had to tweak our message types to
make it compile, but most of the time it just works.
Very nice library. Documentation is very sparse though, so
learning to use DLangUI often means reading source code of
examples and the lib itself, and sometimes even that's not enough
and you need to learn some Android basics, since it originates
from Android world. But once you learn how to use it, how to
encode what you need in DML (a QML counterpart) or add required
functionality by overriding some method of its class, it's really
great and pleasant to use. Many times I was so happy the source
code is available, first for learning, then for tweaking and
fixing bugs. I've found a few minor bugs and sent a few trivial
fixes that were merged quickly. DLangUI is cross-platform and has
several backends for drawing and font rendering. We're using its
minimal build targeted to use Win32 API (had to tweak dub.json a
bit). We don't use OpenGL, as it's not really guaranteed to work
well on any Windows box. Using just WinAPI makes our app smaller,
more stable and avoids dependencies.
Totally fine if you know what you're doing. Some people say you
can't make responsive GUI apps in GC-ed languages. That's a myth.
In this application we rely on GC almost as freely as one would
in C#, allocate strings, messages, widgets and other small litter
without having to worry about deallocation, and it works well,
I've never seen any performance problems related to GC in this
app, and no GC pauses were visible at all. However this is a
32-bit app and some care must be taken to avoid excessive memory
use. Firstly and mainly, where bitmaps for GUI elements and video
frames are allocated. DLangUI tends to allocate everything in GC
heap without second thought and has been allocating some arrays
even just to draw some pictures rescaled. If you're resizing a
window and it has some big bitmap that gets resized too, by
default DLangUI tends to just allocate a new buffer for each new
size, this does not look good in memory section of Task Manager.
However if instead of allocating a new ColorDrawBuf, for example,
you use its resize() method and don't forget to call
assumeSafeAppend() for its buffer, then it stops eating memory
and behaves well, even though it's still "managed", no manual
management required. In couple of places I did change ordinary
arrays to std.container.array to reduce allocations, the code did
not change much but there was much less work for GC. One such
change where it was important (allocation during bitmap drawing)
was merged back to DLangUI, so don't worry about that one.
To deal with video (reading, parsing, decoding, encoding..) we
use DirectShow which is COM-based. I've found a lot of good stuff
for working with COM in VisualD sources. There is IDL2D utility
that converts IDL files from Windows SDK to D source files. We
used it actively (~2K lines generated). There is also TLB to IDL
converter if you need it (I haven't tried to use it myself). The
way it converts COM interfaces, it adds their IIDs (GUIDs) as a
static member of the interface, so when you need to
QueryInterface() you don't need to provide IID for the interface,
it's already there, and this is used by the ComPtr smart pointer
that deals with most COM stuff like reference counting too. I
borrowed initial ComPtr implementation from VisualD and then
changed it a lot, most importantly, my version also checks for
errors automatically, now I have Error Monad for free:
D features used.
Apart from the smart pointer above, we used compile-time
introspection to pass and automatically dispatch messages between
two processes, there is a blog post about that too. We used User
Defined Attributes to describe what to do with errors if they
arise in message handlers
and then proper error handling was performed automatically, no
need to repeat it in each method, just add one word of annotation
and it works.
We used std.concurrency message passing to talk between GUI and
We enjoyed the ability to call C++ interfaces directly from D and
D methods from C++, no FFI required, that was really nice and
helped a lot.
Ability to include binary data as simple as import("file.dat")
was also very nice. This way we include some images and also
bytecode for a little VM, generated by a compiler written in
OCaml, but that is another story.
That's what comes to mind now, the rest of the code is quite
boring I guess.
TL;DR: at least in some areas D is a fine successor to C++ and
can be used to make real world video processing apps that people
around the world use and pay for.