How to be more careful about null pointers?

[cy via Digitalmars-d-learn]

On Monday, 28 March 2016 at 21:24:48 UTC, Adam D. Ruppe wrote:
> If it didn't give the error, either you swallowed it or you 
> didn't actually dereference null.

Okay, so it's not actually supposed to happen. Hopefully it's 
something I did wrong...

> What is the db library you are using? Did you compile it along 
> with your program or use a .lib with it?

d2sqlite3: https://github.com/biozic/d2sqlite3

Compiled it along with my program. And "Database.prepare" is 
neither static, nor final. I keep describing it wrong though, 
what I ended up doing. It's easier to just write a program to 
describe it. What I ended up doing was like this:

struct Database {
   string derp;
   Statement prepare(string s) {
	return Statement(1234);
   }
}

struct Statement {
   int member;
   void bind(int column, int value) {
	import std.stdio;
	writeln("derp",member);
   }

}


class Wrapper {
   Database something;
   Statement prep;
   this() {
     something = Database("...");
     prep = something.prepare("...");
   }
}

Wrapper oops;
void initialize() {
   oops = new Wrapper();
}

class Entry {
   Wrapper parent;
   this(Wrapper parent) {
     //this.parent = parent;
     //oops
     parent = parent;
   }
   void usefulmethod() {
     parent.prep.bind(1,42);
     //parent.prep.execute();
     //parent.prep.reset();
   }
}

void main() {
   initialize();
   auto entry = new Entry(oops);
   entry.usefulmethod();
}

That program causes a segmentation fault on my machine. Somehow 
despite never initializing Entry.parent, a class object (whose 
default init is a null pointer), I can still call methods on it, 
access members on it, and call methods on those members. No 
warnings or errors. The segfault doesn't happen until the bind() 
method.