Reddit: why aren't people using D?

[Andrei Alexandrescu]

Rainer Deyke wrote:
> Walter Bright wrote:
>> Rainer Deyke wrote:
>>> The reason I have stuck with C++ despite its (massive, obvious) flaws is
>>> that it has a couple of really nice and useful features that very few
>>> other languages have even attempted to match.  D is the only language I
>>> know that even tries, although it still falls short in many areas.
>> Fair enough. What are those two features?
> 
> 1. C++'s object model, complete with polymorphic value types,

What designs make good use of polymorphic value types?

> deterministic destructors,  arbitrary copy constructors, and optional
> lack of default constructor.

Struct have that except for default constructor. In D, currently default 
constructors cannot execute code. This is a limitation that we might 
need to address, although it has some advantages.

> D's structs come close, but I think the
> class/struct split hurts D more than it helps.  And, yes, C++ has a lot
> of room for improvement here.

How does the class/struct split? I think it's an enormous source of 
confusion for C++. C++ lore clarifies that you must decide in day one 
whether a class is meant to be polymorphic or monomorphic. Unfortunately 
that can't be expressed in the language, hence the weird cases with 
deriving from std::vector or getting polymorphic values unceremoniously 
sliced. Avoiding such mistakes are important things that C++ users must 
learn because there's nothing in the language stopping them from doing 
such nonsensical things; D very elegantly breaks that pattern by 
defining the language to only allow meaningful constructs.

Who says the class/struct situation is worse off in D than in C++ either 
doesn't know C++ or knows C++ too well.


Andrei