Re: Regarding Design Pattern
On 2011-11-30 06:31:53 +0000, Henning Follmann said:
You mix things up here.
A global variable is a "code organization/accessibility" concept. That
is scope.
Bad about this is the visibility of the _name_ of a variable, what potentially
can lead to multiple declarations.
Just think of "i" as the most common used index in loops. If this a global
scoped variable then you would be in trouble if a loop in a loop uses
this global "i" in both places.
That's one possible problem. But the biggest problem with global data
is that it can be modified from anywhere in the program. Tracking down
a stray modification can be very difficult.
But object-oriented programming makes that less of a problem. If you
confine yourself to modification through member functions (i.e. don't
mess with the data directly), then stray modifications are easier to
find -- just set a breakpoint on the function(s) that do(es) the
modification.
But a singleton most likely is a container fo some information, which will be
used in more than just one place. So you have a single source of information
it has to be globally accessible.
Yes, that's the other side: some data simply has to be available in
several places. Passing it around everywhere in case it's needed is
tedious, bulky, and ugly.
--
Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com) Author of "The
Standard C++ Library Extensions: a Tutorial and Reference
(www.petebecker.com/tr1book)
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