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May 27, 2010
Finding and invoking struct destructors in D2
Hi, all,

I was wondering if there's any way to determine at compile time
whether a struct has a (non-trivial) destructor associated with it,
and whether there's any way to call that destructor without using
the delete operator. It seems like being able to do these two
things would allow you to make a container that plays well with
structs that are designed to do (say) reference counting, but I
don't see anything in the spec on the website that shows how this
might be accomplished.

Thanks!
Pillsy
May 27, 2010
Re: Finding and invoking struct destructors in D2
Pillsy wrote:
> Hi, all,
> 
> I was wondering if there's any way to determine at compile time
> whether a struct has a (non-trivial) destructor associated with it,
> and whether there's any way to call that destructor without using
> the delete operator. It seems like being able to do these two
> things would allow you to make a container that plays well with
> structs that are designed to do (say) reference counting, but I
> don't see anything in the spec on the website that shows how this
> might be accomplished.
> 
> Thanks!
> Pillsy

Struct and class destructors are called __dtor.
This is undocumented though and therefore not guaranteed to work in
future versions or other(!) implementations:

struct foo {
	~this()
	{
	}
}

int main(){

	foo	b;

	static if(__traits(compiles, b.__dtor()))
	{
		pragma (msg, "got destructor");
	}
	else
	{
		pragma (msg, "no destructor");
	}

	return 0;
}


There are various struct destructor bugs still open though, so I
wouldn't count on being able to do a ref counted objects at the moment:

Most important is this one, which scuppers any change of doing a shared
ptr like struct:

http://d.puremagic.com/issues/show_bug.cgi?id=3516

- --
My enormous talent is exceeded only by my outrageous laziness.
http://www.ssTk.co.uk
May 27, 2010
Re: Finding and invoking struct destructors in D2
== Quote from div0 (div0@users.sourceforge.net)'s article:
[...]
> Most important is this one, which scuppers any change of doing
> a shared ptr like struct:

> http://d.puremagic.com/issues/show_bug.cgi?id=3516

Yeah, that basically kills the idea until the bug is fixed. :(

Once it is, I think a hasDestructor template would be a good thing
to have in the standard library.

Cheers,
Pillsy
May 27, 2010
Re: Finding and invoking struct destructors in D2
div0 wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> Pillsy wrote:
>> Hi, all,
>>
>> I was wondering if there's any way to determine at compile time
>> whether a struct has a (non-trivial) destructor associated with it,
>> and whether there's any way to call that destructor without using
>> the delete operator. It seems like being able to do these two
>> things would allow you to make a container that plays well with
>> structs that are designed to do (say) reference counting, but I
>> don't see anything in the spec on the website that shows how this
>> might be accomplished.
>>
>> Thanks!
>> Pillsy
> 
> Struct and class destructors are called __dtor.
> This is undocumented though and therefore not guaranteed to work in
> future versions or other(!) implementations:
> 
> struct foo {
> 	~this()
> 	{
> 	}
> }
> 
> int main(){
> 
> 	foo	b;
> 
> 	static if(__traits(compiles, b.__dtor()))
> 	{
> 		pragma (msg, "got destructor");
> 	}
> 	else
> 	{
> 		pragma (msg, "no destructor");
> 	}
> 
> 	return 0;
> }
> 
> 
> There are various struct destructor bugs still open though, so I
> wouldn't count on being able to do a ref counted objects at the moment:
> 
> Most important is this one, which scuppers any change of doing a shared
> ptr like struct:
> 
> http://d.puremagic.com/issues/show_bug.cgi?id=3516

Yup, that's #3 on my list of Ten Must-fix Bugs.

This related one is pretty bad too.
> http://d.puremagic.com/issues/show_bug.cgi?id=3323

> 
> - --
> My enormous talent is exceeded only by my outrageous laziness.
> http://www.ssTk.co.uk
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