Ios Design Patterns
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Component Design Recall: Problem with Subclassing
the gamedesigninitiative at cornell university Lecture 8 Component Design Recall: Problem with Subclassing Games have lots of classes Each game entity is different NPC Needs its own functionality (e.g. object methods) Human Orc Want to avoid redundancies Makes code hard to change Common source of bugs Human Human Orc Orc Warrior Archer Warrior Archer Might be tempted to subclass Common behavior in parents Redundant Behavior Specific behavior in children the gamedesigninitiative 2 Architecture Patterns at cornell university Recall: Problem with Subclassing Games have lots of classes Each game entity is different NPC Needs its own functionality (e.g. object methods) Warrior Archer Want to avoid redundancies Makes code hard to change Common source of bugs Human Orc Human Orc Warrior Warrior Archer Archer Might be tempted to subclass Common behavior in parents Redundant Behavior Specific behavior in children the gamedesigninitiative 3 Architecture Patterns at cornell university Alternative: Decorator Pattern New Functionality OriginalReference to Original Request Decorator Object Functionalitybase object Object the gamedesigninitiative 4 Architecture Patterns at cornell university Alternate: Delegation Pattern Original Reference to Request Delegate Object delegate Object Forward Request Inversion of the Decorator Pattern the gamedesigninitiative 5 Architecture Patterns at cornell university Issues with Static Typing Method in original class Original object class obj.request(arg1,…, argn) Original Reference to Request Delegate -
The Future of Embedded Software
The Future of Embedded Software Edward A. Lee Professor, Chair of EE, and Associate Chair of EECS UC Berkeley ARTEMIS 2006 Annual Conference Graz, Austria May 22-24, 2006 Why Embedded Software? Why Now? “Information technology (IT) is on the verge of another revolution. Driven by the increasing capabilities and ever declining costs of computing and communications devices, IT is being embedded into a growing range of physical devices linked together through networks and will become ever more pervasive as the component technologies become smaller, faster, and cheaper... These networked systems of embedded computers ... have the potential to change radically the way people interact with their environment by linking together a range of devices and sensors that will allow information to be collected, shared, and processed in unprecedented ways. ... The use of [these embedded computers] throughout society could well dwarf previous milestones in the information revolution.” National Research Council Report Embedded Everywhere Lee, Berkeley 2 The Key Obstacle to Progress: Gap Between Systems and Computing | Traditional dynamic systems theory needs to adapt to better account for the behavior of software and networks. | Traditional computer science needs to adapt to embrace time, concurrency, and the continuum of physical processes. Lee, Berkeley 3 The Next Systems Theory: Simultaneously Physical and Computational The standard model: Embedded software is software on small computers. The technical problem is one of optimization (coping with limited resources). The Berkeley model: Embedded software is software integrated with physical processes. The technical problem is managing time and concurrency in computational systems. Lee, Berkeley 4 Obstacles in Today’s Technology: Consider Real Time Electronics Technology Delivers Timeliness… … and the overlaying software abstractions discard it. -
Game Architecture Revisited Recall: the Game Loop
the gamedesigninitiative at cornell university Lecture 8 Game Architecture Revisited Recall: The Game Loop Receive player input Process player actions Update 60 times/s Process NPC actions Interactions (e.g. physics) = 16.7 ms Cull non-visible objects Transform visible objects Draw Draw to backing buffer Display backing buffer the gamedesigninitiative 2 Architecture Revisited at cornell university The Game Loop Receive player input Process player actions Update Process NPC actions Interactions (e.g. physics) Almost everything is in loop Draw Except asynchronous actions Is enough for simple games How do we organize this loop? Do not want spaghetti code Distribute over programmers the gamedesigninitiative 3 Architecture Revisited at cornell university Model-View-Controller Pattern Controller Calls the • Updates model in methods of response to events • Updates view with model changes Model View • Defines/manages • Displays model the program data to the user/player • Responds to the • Provides interface controller requests for the controller the gamedesigninitiative 4 Architecture Revisited at cornell university The Game Loop and MVC Model: The game state Value of game resources Location of game objects Update View: The draw phase Rendering commands only Major computation in update Draw Controller: The update phase Alters the game state Vast majority of your code the gamedesigninitiative 5 Architecture Revisited at cornell university Application Structure Root Controller Ownership Subcontroller Subcontroller View Model Model -
1. Domain Modeling
Software design pattern seminar sse, ustc Topic 8 Observer, Mediator, Facade Group K 1. The observer pattern (Behavioral pattern, chapter 16 and 17) 1) the observer is an interface or abstract class defining the operations to be used to update itself 2) a solution to these problems A. Decouple change and related responses so that such dependencies can be added or removed freely and dynamically 3) solution A. Observable defines the operations for attaching, de-attaching and notifying observers B. Observer defines the operations to update itself 4) liabilities A. Unwanted concurrent update to a concrete observable may occur Figure 1 Sample Observer Pattern 2. The mediator pattern (Behavioral pattern, chapter 16 and 17) 1) the mediator encapsulates how a set of objects interact and keeps objects from referring to each other explicitly 2) a solution to these problems A. a set of objects communicate in well-defined but complex ways. The resulting interdependencies are unstructured and difficult to understand B. reusing an object is difficult because it refers to and communicates with many other objects C. a behavior that's distributed between several classes should be customizable without a lot of subclassing 3) solution A. Mediator defines an interface for communicating with Colleague objects, knows the colleague classes and keep a reference to the colleague objects, and implements the communication and transfer the messages between the colleague classes 1 Software design pattern seminar sse, ustc B. Colleague classes keep a reference to its Mediator object, and communicates with the Mediator whenever it would have otherwise communicated with another Colleague 4) liabilities A. -
Framework Overview with UML Diagrams
Framework Overview with UML Diagrams Learn to Build Robust, Scalable and Maintainable Applications using PureMVC Framework Overview This document discusses the classes and interfaces of the PureMVC framework; illustrating their roles, responsibilities and collaborations with simple UML (Unified Modeling Language) diagrams. The PureMVC framework has a very narrow goal. That is to help you separate your application’s coding concerns into three discrete tiers; Model, View and Controller. In this implementation of the classic MVC design meta-pattern, the application tiers are represented by three Singletons (a class where only one instance may be created). A fourth Singleton, the Façade, simplifies development by providing a single interface for communications throughout the application. The Model caches named references to Proxies, which expose an API for manipulating the Data Model (including data retrieved from remote services). The View primarily caches named references to Mediators, which adapt and steward the View Components that make up the user interface. The Controller maintains named mappings to Command classes, which are stateless, and only created when needed. The Façade initializes and caches the Core actors (Model, View and Controller), and provides a single place to access all of their public methods. AUTHOR: Cliff Hall <[email protected]> LAST MODIFIED: 3/05/2008 Façade and Core The Façade class makes it possible for the Proxies, Mediators and Commands that make up most of our final application to talk to each other in a loosely coupled way, without having to import or work directly with the Core framework actors. When we create a concrete Façade implementation for our application, we are able to use the Core actors ‘out of the box’, incidental to our interaction with the Façade, minimizing the amount of API knowledge the developer needs to have to be successful with the framework. -
Object-Oriented Analysis, Design and Implementation
Undergraduate Topics in Computer Science Brahma Dathan Sarnath Ramnath Object-Oriented Analysis, Design and Implementation An Integrated Approach Second Edition Undergraduate Topics in Computer Science Undergraduate Topics in Computer Science (UTiCS) delivers high-quality instruc- tional content for undergraduates studying in all areas of computing and information science. From core foundational and theoretical material to final-year topics and applications, UTiCS books take a fresh, concise, and modern approach and are ideal for self-study or for a one- or two-semester course. The texts are all authored by established experts in their fields, reviewed by an international advisory board, and contain numerous examples and problems. Many include fully worked solutions. More information about this series at http://www.springer.com/series/7592 Brahma Dathan • Sarnath Ramnath Object-Oriented Analysis, Design and Implementation An Integrated Approach Second Edition 123 Brahma Dathan Sarnath Ramnath Department of Information and Computer Department of Computer Science Science and Information Technology Metropolitan State University St. Cloud State University St. Paul, MN St. Cloud, MN USA USA Series editor Ian Mackie Advisory Board Samson Abramsky, University of Oxford, Oxford, UK Karin Breitman, Pontifical Catholic University of Rio de Janeiro, Rio de Janeiro, Brazil Chris Hankin, Imperial College London, London, UK Dexter Kozen, Cornell University, Ithaca, USA Andrew Pitts, University of Cambridge, Cambridge, UK Hanne Riis Nielson, Technical University of Denmark, Kongens Lyngby, Denmark Steven Skiena, Stony Brook University, Stony Brook, USA Iain Stewart, University of Durham, Durham, UK A co-publication with the Universities Press (India) Private Ltd., licensed for sale in all countries outside of India, Pakistan, Bhutan, Bangladesh, Sri Lanka, Nepal, The Maldives, Middle East, Malaysia, Indonesia and Singapore. -
Design Patterns in PHP and Laravel — Kelt Dockins Design Patterns in PHP and Laravel
Design Patterns in PHP and Laravel — Kelt Dockins Design Patterns in PHP and Laravel Kelt Dockins [email protected] Design Patterns in PHP and Laravel Kelt Dockins Dolph, Arkansas USA ISBN-13 (pbk): 978-1-4842-2450-2 ISBN-13 (electronic): 978-1-4842-2451-9 DOI 10.1007/978-1-4842-2451-9 Library of Congress Control Number: 2016961807 Copyright © 2017 by Kelt Dockins This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. Trademarked names, logos, and images may appear in this book. Rather than use a trademark symbol with every occurrence of a trademarked name, logo, or image we use the names, logos, and images only in an editorial fashion and to the benefit of the trademark owner, with no intention of infringement of the trademark. The use in this publication of trade names, trademarks, service marks, and similar terms, even if they are not identified as such, is not to be taken as an expression of opinion as to whether or not they are subject to proprietary rights. While the advice and information in this book are believed to be true and accurate at the date of publication, neither the authors nor the editors nor the publisher can accept any legal responsibility for any errors or omissions that may be made. -
Design Specification for Delegation and Incentives in Cardano
Engineering Design Specification for Delegation and Incentives in Cardano–Shelley AN IOHK TECHNICAL REPORT Philipp Kant Lars Brunjes¨ Duncan Coutts [email protected] [email protected] [email protected] [email protected] April 11, 2019 Abstract This document describes the requirements and design for a delegation and incentives mechanism to be used in the Shelley release of Cardano. List of Contributors Lars Brunjes,¨ Jared Corduan, Duncan Coutts, Philipp Kant, Dimitris Karakostas, Aggelos Kiayias, Elias Koutsoupias, Mario Larangeira, Damian Nadales, Aikaterini-Panagiota Stouka. Contents 1 Purpose 4 2 Requirements 5 2.1 Functional Requirements . .5 2.1.1 Proof of Eligibility . .5 2.1.2 Visibility of Delegation on the Blockchain . .5 2.1.3 Restricting Chain Delegation . .5 2.1.4 Cheap Re-Delegation . .5 2.1.5 Neutral Addresses . .5 2.2 Security Requirements . .6 2.2.1 Sybil Attack Protection at Stake Pool Level . .6 2.2.2 Address Non-malleability . .6 2.2.3 Public Spending Keys Should not be Disclosed Prematurely . .6 2.2.4 Mitigate Key Exposure . .6 2.2.5 Handle Inactive Stake Pools . .6 2.2.6 Avoid Hard Transition . .6 2.2.7 Change Delegation Without Spending Key . .7 2.3 Non-functional Requirements . .7 2.3.1 Asymptotic space and time complexity . .7 2.3.2 Minimise economic attacks . .7 2.4 Requirements to Preserve Existing Features . .7 2.4.1 Master Recovery Key . .7 1 2.4.2 Address Recognition . .7 2.4.3 Wallet should be Runnable on Independent Devices . .7 2.4.4 Maintain Privacy . -
Process Synchronisation Background (1)
Process Synchronisation Background (1) Concurrent access to shared data may result in data inconsistency Maintaining data consistency requires mechanisms to ensure the orderly execution of cooperating processes Producer Consumer Background (2) Race condition count++ could be implemented as register1 = count register1 = register1 + 1 count = register1 count- - could be implemented as register2 = count register2 = register2 - 1 count = register2 Consider this execution interleaving with ―count = 5‖ initially: S0: producer execute register1 = count {register1 = 5} S1: producer execute register1 = register1 + 1 {register1 = 6} S2: consumer execute register2 = count {register2 = 5} S3: consumer execute register2 = register2 - 1 {register2 = 4} S4: producer execute count = register1 {count = 6 } S5: consumer execute count = register2 {count = 4} Solution: ensure that only one process at a time can manipulate variable count Avoid interference between changes Critical Section Problem Critical section: a segment of code in which a process may be changing Process structure common variables ◦ Only one process is allowed to be executing in its critical section at any moment in time Critical section problem: design a protocol for process cooperation Requirements for a solution ◦ Mutual exclusion ◦ Progress ◦ Bounded waiting No assumption can be made about the relative speed of processes Handling critical sections in OS ◦ Pre-emptive kernels (real-time programming, more responsive) Linux from 2.6, Solaris, IRIX ◦ Non-pre-emptive kernels (free from race conditions) Windows XP, Windows 2000, traditional UNIX kernel, Linux prior 2.6 Peterson’s Solution Two process solution Process Pi ◦ Mutual exclusion is preserved? ◦ The progress requirements is satisfied? ◦ The bounded-waiting requirement is met? Assumption: LOAD and STORE instructions are atomic, i.e. -
The Problem with Threads
The Problem With Threads Edward A. Lee Robert S. Pepper Distinguished Professor and Chair of EECS UC Berkeley -and - Senior Technical Adviser, director, and co-founder of BDTI Class #: ESC-211 Embedded Systems Conference (ESC) Tuesday, 3 April 2007 Concurrency in Software Practice, As of 2007 | Component technologies z Objects in C++, C#, or Java z Wrappers as service definitions | Concurrency z Threads (shared memory, semaphores, mutexes, …) z Message Passing (synchronous or not, buffered, …) | Distributed computing z Distributed objects wrapped in web services, Soap, CORBA, DCOM, … Lee, Berkeley & BDTI 2 z1 Observations Threads and objects dominate SW engineering. z Threads: Sequential computation with shared memory. z Objects: Collections of state variables with procedures for observing and manipulating that state. Even distributed objects create the illusion of shared memory through proxies. z The components (objects) are (typically) not active. z Threads weave through objects in unstructured ways. z This is the source of many software problems. Lee, Berkeley & BDTI 3 The Buzz “Multicore architectures will (finally) bring parallel computing into the mainstream. To effectively exploit them, legions of programmers must emphasize concurrency.” The vendor push: “Please train your computer science students to do extensive multithreaded programming.” Lee, Berkeley & BDTI 4 z2 Is this a good idea? Lee, Berkeley & BDTI 5 My Claim Nontrivial software written with threads, semaphores, and mutexes are incomprehensible to humans. Lee, Berkeley & BDTI 6 z3 To Examine the Problems With Threads and Objects, Consider a Simple Example “The Observer pattern defines a one-to-many dependency between a subject object and any number of observer objects so that when the subject object changes state, all its observer objects are notified and updated automatically.” Design Patterns, Eric Gamma, Richard Helm, Ralph Johnson, John Vlissides (Addison-Wesley Publishing Co., 1995. -
Dependency Injection in Unity3d
Dependency Injection in Unity3D Niko Parviainen Bachelor’s thesis March 2017 Technology, communication and transport Degree Programme in Software Engineering Description Author(s) Type of publication Date Parviainen, Niko Bachelor’s thesis March 2017 Language of publication: English Number of pages Permission for web publi- 57 cation: x Title of publication Dependency Injection in Unity3D Degree programme Degree Programme in Software Engineering Supervisor(s) Rantala, Ari Hämäläinen, Raija Assigned by Psyon Games Oy Abstract The objective was to find out how software design patterns and principles are applied to game development to achieve modular design. The tasks of the research were to identify the dependency management problem of a modular design, find out what the solutions offered by Unity3D are, find out what the dependency injection pattern is and how it is used in Unity3D environment. Dependency management in Unity3D and the dependency injection pattern were studied. Problems created by Unity3D’s solutions were introduced with examples. Dependency in- jection pattern was introduced with examples and demonstrated by implementing an ex- ample game using one of the available third-party frameworks. The aim of the example game was to clarify if the use of dependency injection brings modularity in Unity3D envi- ronment and what the cost of using it is. The principles of SOLID were introduced with generic examples and used to assist depend- ency injection to further increase the modularity by bringing the focus on class design. Dependency injection with the help of SOLID principles increased the modularity by loosely coupling classes even though slightly increasing the overall complexity of the architecture. -
Singleton Pattern: Motivation • Sometimes Need an Object That Is Unique – There Will Only Be a Single Instance of the Class
Singleton Pattern: Motivation • Sometimes need an object that is unique { There will only be a single instance of the class • Could be done with a global variable, BUT { Such an instance would exist for the duration of the program { If the instance were resource-intensive, this could be a problem { It would be better to create such an object only on an as-needed basis 1 Singleton Pattern: Defined • Singleton Pattern (177): Ensures a class has only one instance, and provides a global point of access to it. • The class manages a single instance of itself. • No other classes can create an instance of a singleton on their own. { I.e., another class cannot execute newInstance = new SingletonClass() • The singleton provides the means for other classes to access the instance. • Class diagram: • The question is: How to implement this so that we can insure that no more than one instance can be created? 2 Singleton Pattern: Implementation • We know that if we have a public constructor for a class, instances can be created by any other classes • But if we make the constructor private, only objects of the class could call the constructor, but then how could a first object of the class be created? { I.e., The only way to create an object of the class is to already have an object of the class (chicken and egg problem) • The trick is to have a private constructor but a static method that creates instances of the class { Since we're dealing with a singleton, the static method will include code that insures that only a single instance of the class will be created • Sample code: public class Singleton { private static Singleton uniqueInstance; private Singleton() { } public static Singleton getInstance() { if (uniqueInstance == null) uniqueInstance = new Singleton(); return uniqueInstance; } ..