fancyvendingmachine.cpp File Reference

Sophisticated Vending Machine example using a Lag-based feedback loop. More...

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Detailed Description

Sophisticated Vending Machine example using a Lag-based feedback loop.

Introduction

You see, here things got a bit out of hand. All I was supposed to do was to code a single representative and fun example. But then I got legitimately nerd-snipped [1] and had to go all the way.

Features

This example provides a vending machine algorithm that keeps track of:

• coin counting
• overlapping-balance purchases
• products in stock
• product prices
• canceling purchases half way through
• change giving (including a solution to the Change-Making problem [2] for non-infinite sets of coins)
• dynamic product refill
• dynamic price updates
• financial report generation

Large TopicState

This example shows a concrete example of how to deal with a Large TopicState - large enough that one wouldn't any unnecessary copies of it. This is the case for the Look-Up Table generated by ChangeAlgo. That table is conveyed inside the ChangeAvailable TopicState to allow for efficient access to properties of that TopicState - namely to check whether change for a given amount can be given. The way this is accomplished is by using a shared_ptr to wrap the heap-allocated Look-Up Table.

Architecture

The graph uses 6 detectors and 14 TopicStates to encode the different logic and data signals.

The 'public' API to this graph is composed of: Inputs:

• CoinInserted
• MoneyBackButton
• SelectedProduct
• RefillProduct
• RefillChange
• PriceUpdate Outputs:
• SaleProcessed
• UserBalance
• ReturnChange
• FinancesReport

The graph below shows the relationships between the topics (rectangles) and detectors (ellipses). Note that this graph can be automatically generated for any instance of DetectorGraph::Graph using DetectorGraph::GraphAnalyzer.

FancyVendingMachine

Other Notes

Note that this entire application in contained in a single file for the sake of unity as an example. In real-world scenarios the suggested pattern is to split the code into:

   detectorgraph/
        include/
            fancyvendingmachine.hpp (FancyVendingMachine header)
        src/
            fancyvendingmachine.hpp (FancyVendingMachine implementation)
        detectors/
            include/
                UserBalanceDetector.hpp
                SaleProcessor.hpp
                ProductStockManager.hpp
                CoinBankManager.hpp
                FinancesReportDetector.hpp
            src/
                UserBalanceDetector.cpp
                SaleProcessor.cpp
                ProductStockManager.cpp
                CoinBankManager.cpp
                FinancesReportDetector.cpp
        topicstates/
            include/
                CoinInserted.hpp
                SelectedProduct.hpp
                SaleProcessed.hpp
                RefillProduct.hpp
                PriceUpdate.hpp
                StockState.hpp
                UserBalance.hpp
                MoneyBackButton.hpp
                ReturnChange.hpp
                FinancesReport.hpp
                RefillChange.hpp
                ReleaseCoins.hpp
                ChangeAvailable.hpp
                CoinType.hpp (enum and GetStr - common core datatypes used
                              across multiple topicstates are also commonly
                              stored here)
                ProductIdType.hpp
            src/
                ChangeAvailable.cpp (TopicStates implementations, as needed)
                CoinType.cpp (e.g GetCoinTypeStr())
                ProductIdType.cpp
        utils/ (For utility modules/algos, as needed)
            include/
                ChangeAlgo.hpp
            src/
                ChangeAlgo.cpp

   Some projects that use Protocol Buffers for its TopicStates may have:
        proto/
            some_data.proto

Although this example makes heavy use of C++11, that is NOT a requirement for DetectorGraph applications.

References

• [1] Nerd Snipping - https://xkcd.com/356/
• [2] Change-Making Problem - https://en.wikipedia.org/wiki/Change-making_problem

Definition in file fancyvendingmachine.cpp.