Any chance to call Tango as Extended Standard Library

[Andrei Alexandrescu]

Lars Ivar Igesund wrote:
> Andrei Alexandrescu wrote:
> 
>> Lars Ivar Igesund wrote:
>>> Andrei Alexandrescu wrote:
>>> 
>>>> Lars Ivar Igesund wrote:
>>>>> Andrei Alexandrescu wrote:
>>>>> 
>>>>>> Lars Ivar Igesund wrote:
>>>>>>> No, you misunderstand. I said safely call, not
>>>>>>> exceptionally efficient. To me a virtual call would be
>>>>>>> acceptable. However, at least in my cases, there would
>>>>>>> normally not be more than one imlemented interface and
>>>>>>> such it would be a tiny vtable.
>>>>>> Ok, so the scope is reducing nicely. We now have a few
>>>>>> problems to solve (some details glossed over for
>>>>>> simplicity).
>>>>>> 
>>>>>> a) Get from void* to the TypeInfo that's typing that void*.
>>>>>> This will involve a search as the void* could point really
>>>>>> anywhere, including untyped memory. So we have a core
>>>>>> function:
>>>>>> 
>>>>>> TypeInfo fromAddress(void * p);
>>>>>> 
>>>>>> b) Starting from a TypeInfo, get an interface in case the 
>>>>>> underlying struct implements that interface:
>>>>>> 
>>>>>> Object TypeInfo.QueryInterface(TypeInfo someInterface);
>>>>>> 
>>>>>> c) Finally, given a void* and an interface, invoke a method
>>>>>> of that interface:
>>>>>> 
>>>>>> T structCast!(Interface)(p).method(arguments);
>>>>> Since you used template lingo, it looks a bit like compile
>>>>> time functionality, but yes, very close now :)
>>>>> 
>>>>> Also (I keep forgetting to mention important details) - I
>>>>> typically see this used in variadic functions, such that the
>>>>> typeinfo already is there.
>>>> But what are you ultimately trying to accomplish, and why do
>>>> you must lose all static information since it was just
>>>> available to the caller? Isn't there a simpler way to achieve
>>>> your goal (e.g. using the new variadics)? You are essentially
>>>> asking for full-blown runtime scripting for all structs.
>>> Sorry; new variadics?
>> http://www.digitalmars.com/d/2.0/variadic-function-templates.html
>> 
>> Your use case suggests you are using the "look, ma, no templates" 
>> solution, whereas the new variadics are shown below that section.
> 
> Right,  but the "new variadics" cannot (being templates) be virtual
> (which at least sometimes is useful).

Templates can always forward to non-templates the void* and pointers to 
functions of interest that know how to handle the void*. The new code in 
std.format does that. The solution can be easily extended to forward to 
interfaces that are created and allocated suitably.

Essentially what I'm saying is, if you're asking for a feature there 
should be a reasonably clear picture of the implementation possible 
attacks and of the various consequences of the tradeoffs involved. I 
understand it would be nice to have structs automatically offer 
runtime-queriable interfaces at no per-instance cost, no dynamic 
allocation, and with free bonus miles, but then that's only a 
deceptively little part of the story.


Andrei