Safest Way to Check a Unit's Existence

Title says it all --
What is the safest and most reliable way to check if a unit exists or not?

GetUnitTypeId(u) != 0 ought to work.

MaxLife() != 0 works also.

It is better to avoid these situations anyways

what about

IsUnitAlive()

?

A unit still "exists" after it dies; a corpse still counts as "existance". Thus, IsUnitAlive() is not sufficient.

i don't understand the question, r u asking whether a unit is dead?

in which case I'd use GetWidgetLife()>.405

or do you care if the unit exists period?

in which case id just see if the unit!=null

Impossible to know with out leaking under general circumstances.

Well, for example.
A unit is removed after it has finished decaying upon death.

I have lots of global variables, and I'd like to do X or Y to them only if they haven't decayed.
I was just seeing if there was a better way than GetWidgetLife() to check if it was removed/there/whatever.
Thanks all.