This is my doubt :
I have two classes A and B.
I can write : 

```
class A: public B  {....}

```

So an\_instance\_of\_A could use B methods .

But I could write also: 

```
class A {
public:
B instance_B;
}

```

So an\_instance\_of\_A could use instance\_B methods. (that is, B methods).

I can do the same. 
What is best ? What is fast to compile ? Is it the same ?
Thanks.