.NET goes
much further:
A routine written in a language L1 may call another routine written in a
different language L2.
A module in L1 may declare a variable whose type is a class declared in
L2, and then call the corresponding L2 routines on that variable.
If both languages are object oriented, a class in L1 can inherit from a
class in L2.
Exceptions triggered by a routine written in L1 and not handled on the L1
side will be passed to the caller, which—if written in L2—will process
it using L2's own exception-handling mechanism.
During a debugging session, you may move freely and seamlessly across modules
written in L1 and L2.
I don't know about you, but I've never seen anything coming even close to this
level of interoperability.
Cached
In software engineering, the singleton pattern is a design pattern that is used to restrict instantiation of a class to one object. This is useful when exactly one object is needed to coordinate actions across the system. The concept is sometimes generalized to systems that operate more efficiently when only one object exists, or that restrict the instantiation to a certain number of objects (say, five). Some consider it an anti-pattern, judging that it is overused, introduces unnecessary limitations in situations where a sole instance of a class is not actually required, and introduces global state into an application.
