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The update here is interesting and may get at the difference of approach between the two modules. (Caveat -- while I know C::A, my exposure to C::P is limited to this thread so far and a quick POD skim, so I may have it wrong. Apologies to the authors if so.) Both modules are effectively just state machines. However, the state-less nature of web-browsing means that tracking state and state transition is a bit more difficult.

The C::A approach with runmodes takes the approach that the runmode specifies a target -- a desired state, or really, a desired action which is usually to reach a certain state. The application reads the desired action from a parameter and dispatches to a subroutine for that action. The subroutine checks the validity of the action given the input and presents a new state back to the user. (This may be done within the runmode subroutine or as a call to a "display_x" subroutine.) Templates really define a state and logic in the templates specialize the state for special cases (e.g. redisplay a form with errors in red). Plus, templates define the the valid state transitions (runmodes) that can be called from a given state.

The C::P approach instead uses the information submitted to the application to determine the state the user was just in rather than the target. (Because of the state-less web, it can't assume that the new request originated from the last state displayed.) The state corresponds to a class, which examines the input to determine an appropriate state transition (from among valid state transitions for that state) and then calls a subroutine in a new class (state) to display back to the user. Classes define how to enter a state -- by displaying a template -- and how to exit -- by executing a state transition for a given input.

Syntax and templating systems aside, this conceptual difference seems to me to be the crux of the issue and preference for use may depend on how a programmer likes to think about it. In C::A, one defines state transitions and uses those to determine a new state to display. In C::P, one defines states and how a user gets from that state to other valid states.

Polymorphism becomes important in C::P as a way of handling special cases (e.g. a form with errors) without repetitive coding, whereas with C::A, the special case coding would more likely happen procedurally in the templates.

Hope that helps some people. (Just writing it was helpful to me to bend my mind around how to conceptualize states and transitions for CGI in general.)

-xdg

Code posted by xdg on PerlMonks is public domain. It has no warranties, express or implied. Posted code may not have been tested. Use at your own risk.


In reply to Re^3: Review: CGI::Prototype by xdg
in thread Review: CGI::Prototype by dragonchild

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