A design pattern is a general reusable solution to a commonly occurring problem in software design.

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PHP - Repository matrix pattern?

I'm trying really hard to refactor some of my legacy code in the project using best practices and design patterns + DDD so I'd love some feedback on an issue I'm currently having. Let's assume that I ...
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0answers
35 views

How do I differentiate between old and new data in backbone collections?

A common pattern I come across is a backbone collection which is initially seeded from a database. However, the user can also add to the collection. When the user does add to the collection, these ...
36
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11answers
5k views

Are error variables an anti-pattern or good design?

In order to handle several possible errors that shouldn't halt execution, I have an error variable that clients can check and use to throw exceptions. Is this an Anti-Pattern? Is there a better way to ...
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2answers
140 views

Expected error handling

Let's say I have a social media website. On this website, users can upload several pieces of information about themselves, including their phone number. To implement this, I have a class called ...
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1answer
87 views

Should state machine with synonym states be shown explicitly?

I am new to state machine modeling and while trying to model a system, I have a question. An example will explain it better: Considering a system that does calling (probably a customized cell phone ...
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1answer
163 views

Technical example of modeling a domain with OOD?

Considering favoring composition over inheritance and looking at various design patterns there are multiple approaches to modeling a domain. Say you have some Entities which are very similar in some ...
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1answer
67 views

Need to provide an interface (for plugins) for taking input Type A, and returning output Type B

public interface IMyInputProviderPlugin { IMyOutput Provide(IMyInput data); } This is an interface I need to provide so that I can dynamically load the dlls and not have them bound to my ...
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0answers
68 views

How to cleanly write a multi step process with user feedback and multiple callback

When you have some process that has several steps and you multiple entry points the code gets ugly pretty fast. I encountered this with Facebook integration in my mobile app: User wants to share ...
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1answer
87 views

delegating program logic to lower-level objects

I'm writing a library for use in scientific computing and ran into a bit of a quandary. The types at work here are a class M which consists of some data and a reference to a container class C. There ...
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1answer
88 views

Testing complex compositions

I have a rather large collection of classes which check and mutate a given data structure. They can be composed via the composition pattern into arbitrarily complex tree-like structures. The final ...
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0answers
189 views

Android From Local DB (DAO) to Server sync (JSON) - Design issue

I sync data between my local DB and a Server. I'm looking for the cleanest way to modelise all of this. I have a com.something.db package That contains a Data Helper and couple of DAO classes that ...
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0answers
73 views

What should a domain object's validation cover?

I'm trying to figure out how to do validation of domain objects that need external resources, such as data mappers/dao Firstly here's my code class User { const INVALID_ID = 1; const ...
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2answers
965 views

Can someone explain in simple terms what is the disruptor pattern?

I would like if you could explain to me in a simple way how does the disruptor patter work. This concept has been elusive to me as of know. Perhaps with your help I could comprehend it.
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1answer
958 views

Why use Android Fragments?

I have read the documentation and some other questions' threads about this topic and I don't really feel convinced; I don't see clearly the limits of use of this technique. Fragments are now seen as ...
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1answer
419 views

How do you show the exception handler in a class diagram?

I have one exception handler class. I want to show this class in the uml -- class diagram. But, I do not know how to represent relationship between class <X> and exception handler class. How can ...
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0answers
81 views

does class reference itself static anti pattern in prism

I have an application and my desing approach look like this: class Manager { public int State; static Manager _instance = null; public static Manager Instance { get { return ...
3
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3answers
214 views

is it valid that a state machine can have more than one possible state for some transition?

I have a requirement for a workflow which I am trying to model as a state machine, I see that there is more than one outcome of a given transition(or activity). Is it valid for a state machine to ...
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2answers
327 views

How to present a stable data model in a public API that allows internal data structures to be changed without breaking the public view of the data?

I am in the process of developing an application that allows users to write C# scripts. These scripts allow users to call selected methods and to access and manipulate data in a document. This works ...
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1answer
202 views

Is there a Design Pattern for preventing dangling references?

I was thinking about a design for custom handles. The thought is to prevent clients from copying around large objects. Now a regular handle class would probably suffice for that, but it doesn't solve ...
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0answers
321 views

What's the best way to expose a Model object in a ViewModel?

In a WPF MVVM application, I exposed my model object into my viewModel by creating an instance of Model class (which cause dependency) into ViewModel. Instead of creating separate VM properties, I ...
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4answers
227 views

Callbacks: when to return value, and when to modify parameter?

When writing a callback, when is best to have the callback return a value, and when is it best to have the callback modify a parameter? Is there a difference? For example, if we wanted to grab a list ...
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0answers
80 views

Processing a list of atomic operations, allowing for interruptions

I'm looking for a design pattern that addresses the following situation: There exists a list of tasks that must be processed. Tasks may be added at any time. Each task is wholly independent from all ...
45
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2answers
5k views

What is the “Free Monad + Interpreter” pattern?

I've seen people talking about Free Monad with Interpreter, particularly in the context of data-access. What is this pattern? When might I want to use it? How does it work, and how would I implement ...
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1answer
55 views

Handling Types for Real and Complex Matrices in a BLAS Wrapper

I come from a C background and I'm now learning OOP with C++. As an exercise (so please don't just say "this already exists"), I want to implement a wrapper for BLAS that will let the user write ...
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1answer
178 views

Does my use of the strategy pattern violate the fundamental MVC pattern in iOS?

I'm about to use the 'strategy' pattern in my iOS app, but feel like my approach violates the somehow fundamental MVC pattern. My app is displaying visual "stories", and a Story consists (i.e. has ...
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5answers
136 views

Preferred way for dealing with customer-defined data in enterprise application

Let's say that we have a small enterprise web (intranet) application for managing data for car dealers. It has screens for managing customers, inventory, orders, warranties and workshops. This ...
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2answers
574 views

How to design console application with good seperation of UI from Logic

Is it considered an overkill for console application to be design like MVC , MVP or N tier architecture? If not which is more common and if you can link me to simple example of it. I want to ...
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3answers
246 views

How to refactor my design, if it seems to require multiple inheritance?

Recently I made a question about Java classes implementing methods from two sources (kinda like multiple inheritance). However, it was pointed out that this sort of need may be a sign of a design ...
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1answer
222 views

Confused about implementing Single Responsibility Principle

Please bear with me if the question looks not well structured. To put you in the context of my issue: I am building an application that invoices vehicles stay duration in a parking. In addition to ...
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2answers
145 views

What are the benefits of using a 'decorator factory' that decorates objects?

In a project I decided to implement the Decorator pattern. I have a class Thing with methodA(), and a class AbstractDecorator that inherits from Thing and that all decorators inherit from: ...
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4answers
3k views

Builder Pattern: When to fail?

When implementing the Builder Pattern, I often find myself confused with when to let building fail and I even manage to take different stands on the matter every few days. First some explanation: ...
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2answers
122 views

Flags with deferred use

Let's say I have a system. In this system I have a number of operations I can do, but all of these operations have to happen as a batch at a certain time, while calls to activate and deactivate these ...
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2answers
229 views

Using packages (gems, eggs, etc.) to create decoupled architectures

The main issue Seeing the good support most modern programming platforms have for package management (think gem, npm, pip, etc), does it make sense to design an application or system be composed of ...
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1answer
134 views

Restructuring a large Chrome Extension/WebApp

I have a very complex Chrome Extension that has gotten too large to maintain in its current format. I'd like to restructure it, but I'm 15 and this is the first webapp or extension of it's type I've ...
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1answer
213 views

Best practice to collect information from child objects

I'm regularly facing following pattern: public abstract class BaseItem { BaseItem[] children; // ... public void DoSomethingWithStuff() { StuffCollection collection = new ...
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126 views

NCurses, scrolling of multiline items, “current item” pointer and “selected items”

I am looking for hints/ideas for the best (most effective) way on how to scroll multi-line items as well as emphasizing of the "current item" and "selected items" such as: 1 FOO ITEM 1 Foo sub-item ...
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0answers
92 views

Is this considered an implementation of the Template Method design pattern?

Please consider a StringBank class. This class holds a list of Strings and can return them to the client. It's code (irrelevant stuff omitted): abstract class StringBank{ List<String> ...
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2answers
243 views

Does this Decorator implementation violate the Liskov Substitution Principle?

Please consider the following implementation of the Decorator design pattern: WordBank objects store strings and return them to the client through the method getWords(). The decorator class, ...
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2answers
253 views

global try-catch in presentation layer

I have a 3-layered app structured as follows. Presentation Layer (ASP.NET MVC project) Business Logic Layer (Services for controllers in PL) Data Access Layer (Repositories) Each Controller in PL ...
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2answers
388 views

Why don't we completely de-couple frontend JS frameworks and backend APIs? [closed]

Whenever we implement a frontend framework in the likes of Backbone, AngularJS etc. there's an integration process involved with the backend technologies like NodeJS, Rails, Yii etc. (like setting up ...
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2answers
485 views

Correct way to inject dependencies in Business logic service?

Currently the structure of my application is as below Web App --> WCF Service (just a facade) --> Business Logic Services --> Repository -> Entity Framework Datacontext Now each of my Business logic ...
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6answers
542 views

Using a Simple/Static Factory vs. instantiating directly: new Thing() vs. factory.createThing() - what's the benefit?

Here are two ways to instantiate an object: Option 1: Thing thing = new Thing(); Option 2: (the factory is a Static Factory, but it could also be a Simple Factory). Thing thing = ...
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1answer
70 views

Algorithmic Forecasting and Pattern Recognition

Say a user could enter project data into my software. Each project has 2 variables "size" and "work" and they're related but the relationship is not known. Is there a way to programmatically determine ...
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1answer
196 views

Correct pattern for Worker Processes involving Queues & Tables

Edit: OK, so, people said it is unclear what I am asking. I am asking for feedback on this design. Here is an example user story: As a group admin on the website I want to be notified when a user in ...
0
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1answer
55 views

Restricting object types that can be added to each other using the Composite Pattern

The Situation: I am building a custom PHP application framework. I have implemented a composite pattern so I can build a object tree representing the page to be rendered. Example: abstract class ...
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1answer
475 views

How is the Decorator Pattern actually used in practice? [closed]

I understand completely how to implement the Decorator pattern, and I also understand what it's intent is. The Decorator is used in one of two cases: As an alternative to subclassing - when there ...
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2answers
156 views

Is using interfaces on internal code a good idea? [duplicate]

I'm working on a set of automated tests that we use internally at work. Lately, we've been designing classes that implement interfaces in addition to inheritance. As I understand it, interfaces in ...
0
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1answer
641 views

pattern to share objects between API and application

I'm having serious doubts about the design for my Web application. I wanted to separate the business logic from the interface so I made a Web API that handles all the requests to the database. It's ...
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1answer
162 views

Adapter Pattern: Design Patterns

So far as I know, there are two forms of the Adapter Pattern: the class adapter and the object adapter. Could someone please explain to me the following limitation of the class adapter and why it is ...
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1answer
85 views

Access items of a container with a pattern

I've two C++ classes with a relation: a container class which has a list of items. For example a library has got many books. The classes are the library and the book. Now from the external world I ...