Accessing members of an array of a class with map.

[Jonathan M Davis via Digitalmars-d-learn]

On Friday, September 30, 2016 19:04:11 Ave via Digitalmars-d-learn wrote:
> An example of what I'm trying to do:
>
> import std.stdio;
> import std.container;
> import std.algorithm;
> class Aa
> {
>      Array!B arrB;
> }
>
> class Bb
> {
>      string name;
>
> }
> void main()
> {
>      Aa test;
>      auto c=new Bb;
>      c.name="asdf";
>      test.arrB.insert(c);
>      auto d=new Bb;
>      d.name="1234";
>      test.arrB.insert(d);
>      writeln(test.arrB[].map!(x=>x.name);
> }
> I was able to get this to compile,but it segfaults.
> If I do this however:
>
> import std.stdio;
> import std.container;
> import std.algorithm;
> class Bb
> {
>      string name;
> }
> void main()
> {
>      Array!B arrB;
>      auto c=new Bb;
>      c.name="asdf";
>      arrB.insert(c);
>      auto d=new Bb;
>      d.name="1234";
>      arrB.insert(d);
>      writeln(arrB[].map!(x=>x.name);
> }
> It will compile and work without seg faulting. What am I doing
> wrong in my first case that's causing the program to seg fault?

The first example is segfaulting, because you never gave the variable, test,
a value. It's null when you try and access its arrB member.

- Jonathan M Davis