Groovy programming with… with

The with method, which is added to all objects by Groovy, “allows the closure to be called for the object reference self.”

This sounds a bit complicated so here are some easy use cases for with:

Setting fields

Many APIs force you to do endless obj.setSomething(something) calls. In Groovy, …

keks.setFoo(someFoo);
keks.setRolf(copter);
keks.setFnuh(guh);

… becomes…

keks.with {
 foo = someFoo
 rolf = copter
 fnuh = guh
}

PROTIP: This works great with the JEE HttpServletRequest and HttpServletResponse classes.

Conditional blocks in which you access another property of the same object can look like this

if (new File('rofl').exists()) {
 assert new File('rofl').length() > 0;
}

or you might be tempted to use a temporary variable

File f = new File('rofl');
if (f.exists()) {
 assert f.length() > 0;
}

neither of which conveys that it’s all about the file. Groovy makes this easier and more readable:

new File('rofl').with {
 if (exists()) {
  assert length() > 0
 }
}

By going with with, you can turn any API, wether it’s fluent or setter-based into one simple, easy-to-read style.