Warning flags during compilation

Compiling the library throws some warnings. Basically 

```bash
delete called on 'XXX' that is abstract but has non-virtual destructor [-Wdelete-non-virtual-dtor]

control reaches end of non-void function [-Wreturn-type]

private field 'XXX' is not used [-Wunused-private-field]

field 'XXX' will be initialized after field '_isGrowing' [-Wreorder]
```

The code needs to be fixed.