null dereference

[luka8088]

I was thinking and I am not sure about the reason for not having some
king of safeguard for null dereferencing in version(assert)/debug builds.

One possible reason that comes to mind is that it somewhat affects
performance but should this really be an issue in version(assert)/debug
build? Especially given the benefit of having file/line number and stack
information outputted.




module program;

import std.stdio;

void main () {

  A a1 = new A();

  // auto inserted by the compiler before accessing object member
  // on version(assert) (or maybe on debug?)
  version(assert)
    if (a1 is null)
      throw new NullDereferenceError("Null Dereference");

  a1.f();

  A a2;

  // auto inserted by the compiler before accessing object member
  // on version(assert) (or maybe on debug?)
  version(assert)
    if (a2 is null)
      throw new NullDereferenceError("Null Dereference");

  a1.f();

}

class A {

  void f () {
    writeln("A.f called");
  }

}

class NullDereferenceError : Error {
  this (string msg, string file = __FILE__, size_t line = __LINE__) {
    super(msg, file, line);
  }
}