D vs C++11

[Malte Skarupke]

On Saturday, 3 November 2012 at 22:45:59 UTC, Tommi wrote:
> On Saturday, 3 November 2012 at 22:01:21 UTC, Malte Skarupke
> wrote:
>>
>> D also makes the const keyword more annoying than it should be.
>
> What kind of annoyances regarding const have you encountered in 
> D?

To start off it's simple things like this:

void main()
{
     struct A
     {
         this(int x) { this.x = x; }
         int x;
     }
     const(A) a = A(5);
     A b = a;
}

This doesn't compile. And it will probably never compile. The 
issue is that struct A has a context pointer and because of 
transitive const, you are not allowed to copy that pointer. And 
you can not specify your own copy constructor because all copy 
constructors happens post-blit, at which point you'd already have 
a non-const pointer. So that will probably never change.

But that's not a big problem.

It's more been stuff like me implementing an equivalent of 
std::function from C++. (as I said I like to be more explicit 
about things than delegates) I uploaded the code for it here: 
http://dpaste.dzfl.pl/60a46049 As you can see there isn't a 
single mention of const in there. All I wanted was a const and an 
immutable version of opCall and better const correctness for 
opAssign, but I just couldn't get it to compile. It'd be great if 
you could have a look at it. If you succeed in getting that code 
to be const correct, please tell me how you did it. (Also worth 
mentioning: I ran into at least two more issues in just this one 
file: 1. I couldn't specify the templated opAssign that C++'s 
std::function has because of a compiler bug (which will be fixed 
in DMD 2.061) and I had to define opAssign twice because there is 
no way to specify a function which accepts both an rvalue and an 
lvalue) That being said the code still is much cleaner than it 
would be in C++.

Another issue I've had was trying to implement my own hashtable 
which has more deterministic memory behavior. In that I found it 
very difficult to get the ranges for byKey and byValue to be 
const correct. I think I had issues with the "inout" keyword when 
I was passing pointers marked as inout to the range object. I 
think I'll revisit that one tomorrow and maybe I'll then post 
code here.