struct Unique(T)

[Namespace]

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