One step out of the TypeInfo stalemate

[Andrei Alexandrescu]

On 7/25/20 12:34 PM, Andrei Alexandrescu wrote:
> I think this has been attempted before. The TypeInfo* classes in 
> object.d are one gnarly thing after another:
> 
> https://github.com/dlang/druntime/blob/master/src/object.d
> 
> Very poor usefulness to real estate ratio, ugly and inefficient 
> implementation, etc. etc.
> 
> One simple step out of this would be to replace TypeInfo_Struct with a 
> template TypeInfo(T) if (is(T == struct)). Then expressions such as 
> `typeid(MyStruct)` would be lowered to 
> `.object.__getTypeInfo!MyStruct()`. That function uses a singleton with 
> lazy allocation.
> 
> That means for all structs the compiler does not need to generate 
> TypeInfo_Struct objects, and the implementation of the primitives is 
> simpler and more efficient.
> 
> We can't do exactly this for classes because typeid(obj) is dynamic, so 
> it requires a virtual call. But there are other ideas we can use there 
> as well.

Progress on this:

https://github.com/dlang/dmd/pull/11459/
https://github.com/dlang/druntime/pull/3172

Next step is to templatize the associative array primitives, which 
resort to horrendous tricks exactly because they lack static type 
information.