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

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pipeline step with two outputs which will be used by different later steps

I am creating a java package which offers an API based on a pipeline pattern. That is I have a series of steps which can be plugged together in any combination provided their inputs match the Output ...
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14 views

How should an entity that abstracts an external service do its operations?

I'm creating a system using some DDD principles and I'm stuck with a problem. To give a bit more of context on what I'm trying to do, let me first describe what the system is about: The ideia is to ...
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82 views

Pattern to use (if any) to co-ordinate loosely coupled classes with strong interdependencies

I have a collection of cooperative classes whose behaviors are interdependent upon one another. But I wish to keep them loosely coupled, so I've created appropriate interfaces. I want to determine an ...
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Unifying database interface for multiple authentication methods

I'm working on a project with Mongo as the db. Currently, we only allow users to sign up with email and we look them up in the db by email address. But now we're moving to allow users to sign up ...
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How do you hash 4 doubles into a size_t?

I have bounding boxes the key type. Box { double mins[2]; double maxs[2]; } And I want to have Box as the key type in the D programming language, so I have to implement: size_t toHash() const ...
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Why avoid Java Inheritance “Extends”

Jame Gosling said “You should avoid implementation inheritance whenever possible.” and instead, use interface inheritance. But why? How can we avoid inheriting the structure of an object using ...
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371 views

Parallel hierarchies - partly same, partly different

There are quite a few similar questions out there 1, 2, 3, 4, but non seems exactly the case in this question, nor do the solutions seem optimal. This is a general OOP question, assuming ...
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2answers
400 views

How can I decouple query and context in a “query object” scenario?

I'm using a query object pattern (similar to this) to manage disparate queries while avoiding bloaded facades/repositories. A query object takes a number of constructor parameters, representing query ...
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38 views

Is there a design pattern to handle construction of complex objects with a [1 → 1..*] multiplicity relationship?

I have two classes (A and B) that are both complex to construct, with multiple properties that must be validated at construction time. I want to use the Builder pattern to construct these objects, but ...
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411 views

Is this a good implementation of the builder pattern? [closed]

I'm trying to design an SQL builder in PHP. I'm trying to make it so that the system could work with different database systems (e.g. Oracle, MySQL, MSSQL). Here's what I've got so far. First, I have ...
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138 views

Function pointers vs. Derived classes

So I have a Signal class and a client class which manages a list of Signal objects. The class provides a bunch of interfaces, one of them is an update()-function. The update()-code is completely ...
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94 views

Interaction between code and user interface

I'm developing a desktop app that has many different algorithms implemented. Some algorithms require additional input from user, this info might not be known before algorithm has started. My ...
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43 views

Repositories, Gateways, Models and Architecture Questions

I am working with a Laravel project and I am looking for a way to solve the issue of bloated models and cross referencing between them. I had started extracting higher level methods to a repository ...
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268 views

Strategy pattern and “Is a” relationship

Imagine, I have class IAlgo which is an interface. I have derived from him and implemented his single method called matchCount in different implementations - AlgoA1, AlgoA2, AlgoA3, AlgoB1, AlgoB2. ...
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2answers
361 views

Scheme/Design Pattern for allowing a certain outside class to set properties

I came up with a solution (in PHP) to a problem and am wondering if it is a named Design Pattern, and if it is good practice. I have a collection class and an item class. The collection class is the ...
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1answer
96 views

What would I call this design pattern in which an overloaded function translates it's arguements type to call a main function? [on hold]

So, I've found I've been using this design pattern fairly frequently, but I'm not sure what to call it if it has a proper name. Essentially there is one "Heavy lifter" function that does some intense ...
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2answers
294 views

Is turning a method into a class to use it across many classes bad practice? [closed]

Let's say I have a sort method inside of my class and another class that has no relationship with that class needs the same method. Instead of writing that method twice and breaking the do not repeat ...
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1answer
315 views

Thoughts on having a generic, reusable grid viewmodel

I'm developing a wpf-based application and I'm currently struggling to find the best way of supporting a recurring scenario in it. This app uses grids a lot. There are a bunch of features I want in ...
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6answers
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Is an event loop just a for/while loop with optimized polling?

I'm trying to understand what an event loop is. Often the explanation is that in the event loop, you do something until you're notified that an event occurred. You than handle the event and continue ...
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2answers
164 views

Is this an appropriate code structure, or is there a better one?

This is an iOS app but I will try to make it as general as possible because I think a wide audience could have good feedback. I have a application I am making for iOS. It has 4 main tabs in a tab bar ...
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1answer
75 views

Respectable design pattern for making node modules flexible/testable?

I am looking to get some input from some more experienced testers than what I am. :) I am trying to make my node modules testable, allowing for dependency spying/stubbing/mocking without the need to ...
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2answers
815 views

How to use SOLID principles in this example

I have reading about SOLID principles last week and decided to try to solve real world problem by using them. So I got the problem of real world ecommerce site managing totals. Problem Statement: ...
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1answer
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Explain ServiceLocator pattern of ZF2

I am looking at this example: http://framework.zend.com/manual/current/en/user-guide/database-and-models.html Relevant excerpt from above: class AlbumController { public function ...
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Is writing your own Data Access / Data Mapping Layer a “good” idea?

We're currently in a situation where we have a choice between using an out-of-the-box object-relational mapper or rolling our own We have a legacy application (ASP.NET + SQL Server) where the ...
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3answers
197 views

Client-Server Application Object with child Objects

Actually I'm going to build an Client Server Application, at the Login I recive the User Object from the Server. An user has a List of tasks, but I don't want to load them at the Login. So what would ...
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Is Module Pattern in JavaScript is useful only for singleton creation?

Some articles (JavaScript Module Pattern In Depth, Mastering The Module Pattern) describe defining modules in JavaScript like in the snippet below (from Addy Osmani's "Learning JavaScript Design ...
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is this a valid javascript design pattern when many instances are required?

I have some code that I'm refactoring, right now its just a list of functions, primarily jQuery. The code is a form builder. The user adds sections, questions etc using jqueryUI drag/drop/sort. They ...
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Why is chaining setters unconventional?

Having chaining implemented on beans is very handy: no need for overloading constructors, mega constructors, factories, and gives you increased readability. I can't think of any downsides, unless you ...
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203 views

Does such a design pattern exist? (Multi-Strategy/Multi-Traits)

Is there a design pattern that would allow a class from a hierarchy to 'subscribe to' concrete methods? For example, say you have an abstract base class that requires the implementation of a method. ...
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709 views

Do I need JUnit tests for the controller layer on a MVC when I have a database layer

I have a MVC which has this structure: ui controller db model Basically the controller doesn't really do much more than connection ui with db layer. Do I need to provide JUnit tests for the ...
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150 views

Object Communication Design

Multiple top-level systems that communicate with each other via messages(events/commands). The Main class of the program wraps around all the systems and has a message dispacher component wich ...
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1answer
83 views

How to represent data objects gradually getting augmented in a pipeline [closed]

I'm working on a Scala data-processing program. Essentially we start with a collection of many small data objects, say, (eventId: String, basicInfo: Basic) and gradually filter out some objects and ...
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50 views

Python Micro-services Architecture

I have a Python-Flask webapp that stores data in MongoDB using an ORM. I want to extend this app and add a Apache Storm based micro-service that will require read & write access to dbs of the ...
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Is using interfaces for datatypes an anti-pattern?

Suppose I have a various entities in my model (using EF), say User, Product, Invoice and Order. I am writing a user control that can can print the summaries of entity objects in my application where ...
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206 views

How should one model an ExchangeService object (in ews-java-api) for sharing MS Exchange connections?

I am creating an application which uses ews-java-api to connect to an MS Exchange server. Once the connection is authenticated, the api dictates use of ExchangeService object for searching mailboxes, ...
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4answers
412 views

Possible way to make java class builder more abstract by using interface required keys

I'm looking for a more abstract pattern for builders that handles required fields without the need of writing a validator that checks if all requried fields are set. I like this builder. But is ...
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MVC - Do I create 'joint' layers when dealing with multiple models?

I'm new to MVC and the different layers architecture and this is what I have currently: 2 models: User, Company 2 service layers: UserService, CompanyService 2 interfaces which abstract the ...
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3k views

What is the difference between Single Responsibility Principle and Separation of Concerns

a)What is the difference between SRP and SoC? Perhaps that SRP is applied at class level, while SoC can be applied at system, subsystem, module, class or function levels. b) If answer to a) is yes, ...
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1answer
92 views

Compiler design prevent register override

I'm trying to write a compiler for a self-designed CPU with accompanying instruction set. The CPU has 3 registers, 2 input registers (B and C) and one output register (D). When for example an ADD ...
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153 views

What design pattern is used in this delegating scenario?

I am currently having to bend some framework API to fit my usecase. The framework provides generic interfaces such as public interface Processor<T> { T process(T t); } with various ...
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Is this a Model or a ViewModel?

In a login screen, a user may expose his username and password data. The same way, in a user list screen, it may expose user name, age, and phone. But none of this views may expose any other user ...
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Design pattern to holds API exchanges?

I'm developing a simple application that crawls in web pages to obtain some information. For this I used and tested some libraries, like crawler4j, jsoup, jaunt and htmlunit. I exchanged several ...
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1answer
155 views

Is there a term for splitting a function into “prep” and “do” halves?

I'm revisiting old code, and I noticed that the main logic is in one method, which is longer than I'd like (~60 lines). So I split it, and there's a natural seam on which to do so: the first half ...
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Laravel Modules based structure [on hold]

I am building a social network app and I have decided to have following features as of now. Meetups / Events (Users will create events and other users will have options to join ) Q / A forum (mini ...
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8answers
633 views

Can “return this” pattern be optimized to no cost performance?

return this (or similar construct) allows method chaining. Lack of it is painful, because you have to write such code (C#): var list = new List<string>(); list.Add("hello"); list.Add("world"); ...
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1answer
100 views

How to implement strategy pattern on N-Tier application? [on hold]

Well, i have a N-Layer MVC project which is something like: Domain > Repository > Application > Presentation I have a feature on the website where the user put some monthly expenses (food, gas, ...
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1answer
76 views

Is IntentService an implementation of Command Pattern?

According to Wikipedia: In object-oriented programming, the command pattern is a behavioral design pattern in which an object is used to encapsulate all information needed to perform an action or ...
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File based communication vs Rest or RPC

My company make automation machines (with a PC inside and a custom built software to control it). So, for the purpose of this question, we can say that these are normal PCs. Sometimes we have the ...
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Using Javascript popups to create a workflow for legal experts writing and editing legislation [migrated]

I suppose this is a ui-flow question. I'm currently working on a project where a couple of the stakeholders are suggesting the use of popup windows, i.e. browser tabs, to create a workflow to ...
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Communication between nested directives

There seem to be quite a few ways of communicating between directives. Say you have nested directives, where the inner directives must communicate something to the outer (e.g. it's been chosen by the ...