std.boxer vs Any

[Bill Baxter]

Daniel Keep wrote:
> 
> Bill Baxter wrote:
>> Daniel Keep wrote:
>>> Bill Baxter wrote:
>>>> Daniel Keep wrote:
>>>>> And just to throw a little more wood on the fire:
>>>>> http://www.prowiki.org/wiki4d/wiki.cgi?DanielKeep/Variant
>>>>>
>>>>> :P
>>>>>
>>>>>     -- Daniel
>>>> Maybe you could comment on what makes yours different/better than the
>>>> alternatives, then.  Do we really need three different versions of this?
>>>>  Are they suited for different purposes?
>>>>
>>>> --bb
>>> Well, the primary difference between mine and std.boxer is that mine
>>> works in Tango out of the box.
>>>
>>> The other reason I wrote it was because of something Pragma posted about
>>> on the Tango forums about making a Box that was easier to use.  The
>>> major improvement is the use of opAssign that allows you to directly
>>> assign to a Variant.  I also like to think that Variant is easier to use
>>> than std.boxer.
>>>
>>> The whole "operator overloading" business was done mostly because I
>>> wanted to see if it *could* be done.  :P
>>>
>>> Really, I think there's only so much you can do with a variant type in
>>> D, and Box and Variant each do about 90% of it (not the *same* 90%, mind
>>> you; Variant doesn't do the "call a vararg function using a Box array"
>>> trick.)  In the case of Box and Variant, the differences are mostly just
>>> implementation and interface issues.
>> Looks like maybe yours avoids the opaque storage gc problem too?
>>
>> --bb
> 
> I doubt it.  One of its members an array, which should mark Variants as
> containing pointers.  The problem is that it's just as valid to store an
> array or pointer in a Variant as it is to store a value like an int or
> float.  Also, since a Variant is a struct, I don't think I can use
> gc.hasNoPointers.
> 
> Making Variant a class would allow one to properly inform the GC what
> kind of data its storing, but then I wanted Variant to be a struct so I
> could use the opAssign trick, not to mention value semantics.
> 
> 	-- Daniel


Ok, so that's a good raison d'etre for Aarti's 'Any' class.  It uses the 
actual type as a template parameter to an inner class that contains 
nothing but the payload, so I think it should be ok.

Seems like you should be able to use the same trick for a struct if you 
don't mind the extra heap alloc on the inside.

--bb