Runtime introspection, or how to get class members at runtime Fin D

[Jacob Carlborg]

On 2018-06-06 15:28, Arafel wrote:
> Hi,
> 
> What is the state of runtime introspection in D, specifically for 
> classes? Is there any way to get *at runtime* the (public or otherwise 
> accessible) members of a class?
> 
> I have had a look as TypeInfo_Class [1], but apparently I can only get a 
> list of types and offsets... which would be almost good enough, if not 
> because the names of the members are missing, or at least I haven't been 
> able to find them.
> 
> In this case, what I'm trying to do is to serialize / dump / print the 
> contents of an object (class instance) without knowing its actual 
> runtime type.
> 
> Before somebody suggests compile time introspection, the "main" code 
> where this routine lives only provides a base class, and it's up to 
> dlopen'ed plugins to provide the actual implementation... so I'm sorry 
> but no compile-time solution can possibly work.
> 
> Also, having each derivative class provide their own dumping information 
> is not practical, I'd rather have it automated.
> 
> I know it might not be the most idiomatic D, but as somebody with mostly 
> a Java background (with some C and just a bit of C++) it seems something 
> really straightforward to me: myObject.getClass().getFields() [2].
> 
> Also, I know I could add some UDA or even crawl the modules and have 
> this information generated automatically at compilation time and added 
> to the type itself in a member, and I might even end up doing it, but 
> honestly, I think it's something that the language should provide in a 
> kind of easy / accessible way.
> 
> Powerful as compile-time introspection is, I think runtime shouldn't be 
> forgotten either :-)

The simplest, in my opinion would be to for the subclasses to register 
themselves with the serializer. This is how Orange works to allow 
serializing through base class references [1]. The use compile time 
introspection on the subclass and serialize that as usual.

[1] 
https://github.com/jacob-carlborg/orange/blob/master/tests/BaseClass.d#L73

-- 
/Jacob Carlborg