Re: GOF - Decorator and STL::Vector

Ulrich Eckhardt <>
Thu, 27 Jul 2006 09:40:23 +0200
<> wrote:

Well, I just finished taking a Design Patterns class at Johns Hopkins
and would like to apply what I have learned.

Beware of the "when you have a hammer, every problem looks like a nail"

Besides that, I'm using the command pattern on a long running
application and the undo stack does not get cleared (ever possibly) so
I would like to limit the size of the stack to something reasonable
like 500 undo operations. I'm using a vector to hold the undo stack
and I don't beleive you can limit its size.

A vector is a bad idea, because you will be erasing elements from the front
when you limit the size. Doing so requires a copy of all other elements
though, so it is not very efficient. Two other containers are better
choices, list and deque, for your job deque will probably be the right
choice, you don't need the added flexibility of being able to insert and
remove in the middle.
Now, I'd suggest you just think about the interface the undo stack should
have first i.e. what operations it needs to support like pushing undo
operations, popping them back and checking whether it is empty. In addition
to perhaps clearing it and configuring its maximal size. Then, you can
implement this interface with whatever container you want.

I'm using Visual Studio 5.0 on Windows 2000/sp 4.0.

Ahem, are you sure? Even Visual Studio 6, which is still rather popular, is
not supported by MS anymore because it is almost ten years old. VS5 is too
far out to learn C++ IMHO.

I thought the decorator would be a good way to modify the vector since
as requirements change I could add more decorators, possible at
runtime, with limited effect on the application.

Don't overcomplicate things. Maybe you need it, maybe you don't, I can't
tell as I don't know your design, but in general prefer simple solutions.
Making things too abstract and giving lots of possibilities and points of
customisation is a bad idea for an application writer (as opposed to a
library writer), don't fall into that trap.


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