By my knowledge I can only call the method of a class only if I instantiate or if the method is static!
I can only do something like class->metodo('var') or class::metodo('var') .
However, I've seen in some code something like class->metodo('var')->outrometodo('') .
Drupal itself uses something similar. Ex:
db_select('node', 'n')->execute()->fetchCol();
How do you make this type of call, and what would be the advantages?