On Feb 21, 2006, at 9:28 PM, Guyren Howe wrote:
On Feb 21, 2006, at 5:57 PM, Joseph J. Strout wrote:
Now that REALbasic 2006 has shared methods and shared properties, is
it possible to have a true Singleton object?
Sure -- but then, it was quite possible before too, except that the
enforcement was at runtime rather than at compile time.
The current shared methods and properties make the class behave like a
module, not like an object (which is what a singleton should be). You
can't store a reference to a class in a data structure, or exploit
polymorphism with its shared methods.
I believe that class methods in C++ behave similarly; this is one of
the standard disadvantages of the standard implementations of
Singleton. If you want polymorphic behavior, then you would want to
use the Monostate version, which couples shared properties with object
methods. In general, just what a Singleton should be is a matter of
ongoing debate. A glib but reasonable resolution is that a Singleton
should be what it needs to be -- overemphasizing the pattern is a case
of the tail wagging the dog.
--------------
Charles Yeomans
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