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

On Thursday, 7 November 2013 at 00:07:25 UTC, ChrisG wrote:
> 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:

I'm pretty sure things like Unique have been neglected for awhile. Probably for a decent reason, but a lot of language features have been landing that could help polish it up a bit more.

> Next, I'd like to be able to use a custom deleter. For example, a naive implementation I could write would be something like:
>
> ... snip ...
>
> 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.

I think Unique will probably be getting something along those lines reasonably shortly, but std.allocator will have to be fully completed first.

http://forum.dlang.org/thread/l4btsk$5u8$1@digitalmars.com

Once that's done we'll see some memory management schemes like what you're suggesting be implemented. But it's probably not a good idea to add that stuff before we figure out a good way to use it with the new std.allocator effectively.

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

On Thursday, 7 November 2013 at 01:09:45 UTC, Chris Cain wrote:
> On Thursday, 7 November 2013 at 00:07:25 UTC, ChrisG wrote:
>> 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:
>
> I'm pretty sure things like Unique have been neglected for awhile. Probably for a decent reason, but a lot of language features have been landing that could help polish it up a bit more.
>
>> Next, I'd like to be able to use a custom deleter. For example, a naive implementation I could write would be something like:
>>
>> ... snip ...
>>
>> 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.
>
> I think Unique will probably be getting something along those lines reasonably shortly, but std.allocator will have to be fully completed first.
>
> http://forum.dlang.org/thread/l4btsk$5u8$1@digitalmars.com
>
> Once that's done we'll see some memory management schemes like what you're suggesting be implemented. But it's probably not a good idea to add that stuff before we figure out a good way to use it with the new std.allocator effectively.

Ok, thanks. That does make some sense to me. I read some of the std.allocator thread. I'll take a look at that code and see what I can make of it.

On Thursday, 7 November 2013 at 09:51:38 UTC, Namespace wrote:
>
> 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

Thanks. I've been looking through your website and github. Very cool stuff. What license is your code released under?

On Thursday, 7 November 2013 at 18:19:35 UTC, ChrisG wrote:
> On Thursday, 7 November 2013 at 09:51:38 UTC, Namespace wrote:
>>
>> 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
>
> Thanks. I've been looking through your website and github. Very cool stuff. What license is your code released under?

Under zlib/png. I should add this on my site and in my code. Thanks for remembering. :)