On Thursday, 7 November 2013 at 00:07:25 UTC, ChrisG wrote:
Hi, I've been following the D language off and on for several
years, have read Andrei's D book, but haven't ever posted here
before. Mostly, I come from a C++ and C# background. Recently,
I was playing with D using the derelict bindings for the SDL
library.
The SDL library uses handles in the form of struct pointers for
resource management. In C++ I like using unique and shared
pointers to manage C handles. Additionally, I like being able
to specify custom clean up functions for specific resources.
For example:
typedef std::unique_ptr<HandleType, HandleDeleter> handle_ptr;
My question is: what's the status of D's struct Unique? It
looks like struct RefCounted is current, but I can't tell with
Unique. There's several comments in the source that say:
doesn't work yet. It seems like some of it could be made to
work as intended. For example, the commented out code to
disallow construction via an lvalue:
// this(U)(ref Unique!(U) u) = null; // commented out
// this(this) = null;
Couldn't this be written:
@disable this(U)(ref Unique!(U) u);
@disable this(this);
Seems to work when I try it. It stopped the copy from working,
but I can still do a move. Like this:
Unique!(int) i1 = new int;
Unique!(int) i2 = move(i1); // works!
Next, I'd like to be able to use a custom deleter. For example,
a naive implementation I could write would be something like:
struct Unique2(T, string D = "delete")
{
...
~this()
{
debug(Unique2) writeln("Unique destructor of ", (_p is
null)? null: _p);
if (_p !is null)
{
mixin(""~D~" (_p);"); // delete _p;
_p = null;
}
}
...
So, I could do things like:
Unique2!(int, "free") i1 = cast(int*)malloc(int.sizeof); //
lame example
A real implementation would allow more interesting deleters in
the form of delegates, but I'm already stretching my D skillz.
Anyway, am I missing something here? Is there a better D
language feature I'm not thinking about that provides the same
functionality as C++'s std::unique_ptr<> with custom deleters;
besides putting scope (exit) everywhere?
-Chris
Dgame use the SDL also and needed therefore (as you do) shared
and unique pointers (mostly shared). So I wrote my own versions
and like to share them with you, maybe it helps you.
Surface with shared SDL_Surface:
https://github.com/Dgame/Dgame/blob/master/Graphics/Surface.d#L67
Creation of the shared_ptr:
https://github.com/Dgame/Dgame/blob/master/Graphics/Surface.d#L100
And the shared_ptr struct:
https://github.com/Dgame/Dgame/blob/master/Internal/Shared.d