Playing with SafeRefCounted

I’ve been playing around with SafeRefCounted, a relatively recent addition to the D programming language. It has some nice features. I could see it being useful to work with/port C code.

One of the things that stands out to me, though, is the fact that you can’t use it in @safe code. It won’t even compile without the -dip1000 flag. Even if it does, you can’t have useful things like opSlice. Seems kind of pointless to have a safe reference counted struct if it doesn’t give you any guarantees of safety. @trusted annotations are ignored, which doesn’t make the slightest bit of sense to me.

Here’s an example that uses it with manually allocated memory to ensure that it’s freed.

import core.stdc.stdlib;
import std.stdio, std.typecons;

void main() {
  auto v = RCArray(5);
  writeln(v[]);
}

double * newArray(long obs) {
  return cast(double*) calloc(obs, double.sizeof);
}

void freeArray(double * x) {
  free(x);
}

struct DoubleArray {
  double * val;
  long n;
  
  this(long _n) {
    val = newArray(_n);
    n = _n;
  }
  
  ~this() {
    writeln("Destroying");
    free(val);
  }
  
  double[] opSlice() {
    return val[0..n];
  }
}
alias RCArray = SafeRefCounted!DoubleArray;

True minimal theme