Compiler patch for runtime reflection

Daniel Gibson metalcaedes at gmail.com
Sat Oct 22 04:57:17 PDT 2011


Am 22.10.2011 05:48, schrieb Robert Jacques:
> On Fri, 21 Oct 2011 17:23:17 -0400, Daniel Gibson
> <metalcaedes at gmail.com> wrote:
>> Am 21.10.2011 21:07, schrieb Vladimir Panteleev:
>>> Hi,
>>>
>>> Igor Stepanov has created a patch for DMD and Druntime which adds RTTI
>>> information for class and struct members.
>>>
>>> Example:
>>>
>>> import std.stdio;
>>>
>>> class Foo
>>> {
>>> static void PrintHello()
>>> {
>>> writeln("Hello");
>>> }
>>> }
>>> void main()
>>> {
>>> auto info = cast(OffsetTypeInfo_StaticMethod)Foo.classinfo.m_offTi[0];
>>> assert(info.name == "PrintHello");
>>> auto print = cast(void function())info.pointer;
>>> print(); //prints "Hello"
>>> }
>>>
>>> While the inclusion of such functionality into the language remains a
>>> disputed matter, would anyone be interested in an unofficial patch for
>>> this?
>>>
>>> Walter: would it be okay if the compiler changes were published as a
>>> GitHub fork, or should we stick to patches?
>>>
>>
>> I'd love to see proper runtime reflection support in D, including
>> functionality to get information about available methods (their name and
>> parameters) and a way to call them.
>
> What do you mean by their 'parameters'? What about overloads?
> Attributes? Arguments? Argument attributes?
>

Primarily arguments. That should help identifying overloads.
But attributes and argument attributes are needed as well.

>> Something that is close to what Java offers would be great.
>
> And what, exactly does JAVA offer? What works? What doesn't work? What's
> missing?

See
http://download.oracle.com/javase/6/docs/api/java/lang/Class.html
You can access constructors (look for one by it's parameters or get all 
of them), the same for methods (methods the class declares and all 
methods, i.e. also inherited ones), implemented interfaces, fields, ...
>
>> BTW: I don't really see the problem with providing this information
>> (overhead-wise) - the information needs to be available once per
>> class/struct, but objects of classes just need one pointer to it (other
>> types don't even need that because they're not polymorphic and - like
>> methods of structs - the address of the information is known at
>> compile-time).
>
> 1) Unused information is simply bloat: it increases exe size, slows the
> exe down and increases the runtime memory footprint.

Yeah, but (mostly) only per class, not per object (besides one pointer 
per object, which shouldn't be that bad and something like this seems is 
already there for the existing typeinfo)

> 2) On a lot of systems (i.e. consoles, embedded, smart phones, tablets)
> memory and disk space are both highly constrained resources that you
> don't want to waste.
> 3) RTTI provides a back-door into a code-base; one that for many reasons
> you may want to keep closed.

Yeah, it may make sense to be able to deactivate it.

Cheers,
- Daniel


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