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• Are There Realistic/Useful Solutions for Source Control for Ladder Logic Programs

  - by Steven A. Lowe

  Version control for ladder logic (LL) programs for programmable logic controllers (PLCs) seems to be virtually non-existent. It may be because LL is a visual language and tends to be stored in binary files, or it may be because source code control hasn't "caught on" in process control engineering circles - or perhaps my Google-Fu is weak tonight. Do you know of any realistic and useful solutions for version control for such systems? Definitions: realistic = changes to the programs are tracked by user and subject to reversion and merges useful = the system integrates with visual LL designers, is not limited to LL from a single PLC manufacturer, and does not cost a ridiculous amount of money? Note: I have heard of people using SVN or Mercurial et al to track the binary files, but I don't think the diff/merge capabilities would display readable differences.

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• What's the ethos of the programming profession?

  - by mac

  I am one of those people who became professional programmer by chance, rather than by choice: I moved to a country whose main language I couldn't speak, I knew how to code... and here I am a few years later. Because of this I never really gave much a thought about the ethos of being a programmer, and working as a freelance I neither had many occasions to discuss this with fellow colleagues. Among others, Dictionary.com define the word ethos as follows: The fundamental character or spirit of a culture; the underlying sentiment that informs the beliefs, customs, or practices of a group or society; dominant assumptions of a people or period. So my question is: How would you describe the ethos of being a programmer, and why would you say so? Please note that: my question is different than this and this other ones (although you might have chosen to become a programmer because of the programmer'ethos or you might think that part of the programmer ethos is about "programming being a meaningful profession"). beside the "how/what" part of the question, there is a "why" part too! :) I would appreciate if the answer could be based not only on the idealised vision of the hero-programmer, but also on real working and life experience. Thank you in advance for your time and contributions!

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• How do you cope with change in open source frameworks that you use for your projects?

  - by Amy

  It may be a personal quirk of mine, but I like keeping code in living projects up to date - including the libraries/frameworks that they use. Part of it is that I believe a web app is more secure if it is fully patched and up to date. Part of it is just a touch of obsessive compulsiveness on my part. Over the past seven months, we have done a major rewrite of our software. We dropped the Xaraya framework, which was slow and essentially dead as a product, and converted to Cake PHP. (We chose Cake because it gave us the chance to do a very rapid rewrite of our software, and enough of a performance boost over Xaraya to make it worth our while.) We implemented unit testing with SimpleTest, and followed all the file and database naming conventions, etc. Cake is now being updated to 2.0. And, there doesn't seem to be a viable migration path for an upgrade. The naming conventions for files have radically changed, and they dropped SimpleTest in favor of PHPUnit. This is pretty much going to force us to stay on the 1.3 branch because, unless there is some sort of conversion tool, it's not going to be possible to update Cake and then gradually improve our legacy code to reap the benefits of the new Cake framework. So, as usual, we are going to end up with an old framework in our Subversion repository and just patch it ourselves as needed. And this is what gets me every time. So many open source products don't make it easy enough to keep projects based on them up to date. When the devs start playing with a new shiny toy, a few critical patches will be done to older branches, but most of their focus is going to be on the new code base. How do you deal with radical changes in the open source projects that you use? And, if you are developing an open source product, do you keep upgrade paths in mind when you develop new versions?

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• Using which technique does facebook and pininterest show images?

  - by manish

  If anybody has ever noticed that when you open a image in Facebook something like this happens:- suppose you are at your homepage on Facebook:- the URL is https://www.facebook.com/ now if you open a image it gets opened in new modal like window and URL changes to:- https://www.facebook.com/photo.php?fbid=10151125374887397&set=a.338008237396.161268.36922302396&type=1&theater As far as I know in any common case a modal overlay would have kept the url in the address bar the same , My question is how does facebook / pintrest achieve this behaviour of not re-loading the whole page but still achieving the change in the address bar. Is there any jquery or javascript plugin for this?

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• MATLAB: Best fitness vs mean fitness, initial range

  - by Sa Ta

  Based on the example of Rastrigin's function. At the plot function, if I chose 'best fitness', on the same graph 'mean fitness' will also be plotted. I understand well about 'best fitness' whereby it plots the best function value in each generation versus iteration number. It will reach value zero after some times. I don't understand about 'mean fitness'in the graph plotted. What do those 'mean fitness' values mean? How does the 'mean fitness' graph help to understand Rastrigin's function? What are the meaning of the term initial population, initial score and initial range? I wish to have a better understanding of these terms. The default value for initial range is [0,1]. Does it mean that 0 is the lower bound (lb) and 1 is the upper bound (ub)? Do these values interfere with the lb and ub values I set in the constraints? I try to better understand about lb and ub. If my lb is 0 and ub is 5, does it mean that my final point values will be within 0 and 5? If I know the lb and ub for my problem is between 0 and 5, do I just set the initial range as [0,5] at all times and may I assume that this is the best option for initial range, and I need not try it with any other values?

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• Is "Interface inheritance" always safe?

  - by Software Engeneering Learner

  I'm reading "Effective Java" by Josh Bloch and in there is Item 16 where he tells how to use inheritance in a correct way and by inheritance he means only class inheritance, not implementing interfaces or extend interfaces by other interfaces. I didn't find any mention of interface inheritance in the entire book. Does this mean that interface inheritance is always safe? Or there are guidlines for interface inheritance?

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• Software Architecture - From design to sucessful implementation

  - by user20358

  As the subject goes; once a software architect puts down the high level design and approach to a software that is to be developed from scratch, how does the team ensure that it is implemented successfully? To my mind the following things will need to be done Proper understanding of requirements Setting down coding practices and guidelines Regular code reviews to ensure the guidelines are being adhered to Revisiting the requirements phase and making necessary changes to design based on client inputs if there are any changes to requirements Proper documentation of what is being done in code Proper documentation of requirements and changes to them Last but not the least, implementing the design via object oriented code where appropriate Did I miss anything? Would love to hear any mistakes that you have learned from in your project experiences. What went wrong, what could have been done better. Thanks for taking the time..

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• Is there or why not having a ruby technology specification similar to Java's JSR?

  - by romeu.hcf

  I think on a community portal where specifications are made, documented and specified to reference libraries and systems implementation. An example: A specification for Message Queue where redis clients, for instance, could implement it and where the libraries could be validated by the specification's test suite. Redic, redis-rb, hiredis, redis-connection-pool, redis-namespace should all implement this specification. This way, being easily replaced.

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• 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?

  - by Max Palmer

  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 well, however, in the development version, scripts access the document's (internal) data structures directly. This means that if we were to change the internal data model/structure, there is a good chance that someone's script will no longer compile. We obviously want to prevent this breaking change from happening, but still want to allow the user to write sensible C# code (whilst not restricting how we develop our internal data model as a result). We therefore need to decouple our scripting API and its data structures from our internal methods and data structures. We've a few ideas as to how we might allow the user to access a what is effectively a stable public version of the document's internal data*, but I wanted to throw the question out there to someone who might have some real experience of this problem. NB our internal document's data structure is quite complex and it could be quite difficult to wrap. We know we want to expose as little as possible in our public API, especially as once it's out there, it's out there for good. Can anyone help? How do scripting languages / APIs decouple their public API and data structures from their internal data structures? Is there no real alternative to having to write a complex interaction layer? If we need to do this, what's a good approach or pattern for wrapping complex data structures that include nested objects, including collections? I've looked at the API facade pattern, which looks like it's trying to address these kinds of issues, but are there alternatives? *One idea is to build a data facade that is kept stable across versions of our application. The facade exposes a set of facade data objects that are used in the script code. These maintain backwards compatibility and wrap access to our internal document's data model.

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• Are too many assertions code smell?

  - by Florents

  I've really fallen in love with unit testing and TDD - I am test infected. However, unit testing is used for public methods. Sometimes though I do have to test some assumptions-assertions in private methods too, because some of them are "dangerous" and refactoring can't help further. (I know, testing frameworks allo testing private methods). So, It became a habit of mine that (almost always) the first and the last line of a private method are both assertions. I guess this couldn't be bad (right ??). However, I've noticed that I also tend to use assertions in public methods too (as in the private) just "to be sure". Could this be "testing duplication" since the public method assumpotions are tested from the unit testng framework? Could someone think of too many assertions as a code smell?

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• API Design Techniques

  - by Dehumanizer

  Is it right or more beautiful to name the functions with an prefix, like in Qt? Or using "many" namespaces, but 'normal' names for functions? For example, slOpenFile(); //"sl" means "some lib" vs some_lib::file_functions::openFile(); UPD: I've read somewhere that the first variant(using some prefix) is better, because the API users can perform 'fast' search among the documentation and in the Internet. E.g. by typing the magic prefix search engine starts to advice the exact functions. Is it enough to use the first variant?

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• Version hash to solve Event Sourcing problems

  - by SystematicFrank

  The basic examples I have seen about Event Sourcing do not deal with out of order events, clock offsets in different systems and late events from system partitions. I am wondering if more polished Event Sourcing implementations rely on a version stamp of modified objects? For example, assuming that the system is rendering the entity Client with version id ABCD1234. If the user modifies the entity, the system will create an event with the modified fields AND the version id reference to which version it applies. Later the event responder would detect out of order events and merge them.

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• Multiple sites with the same codebase in Python

  - by Jimmy

  I am trying to run a large amount of sites which share about 90% of their code. They are simply designed to query an API and return the results. They will have a common userbase / database but will be configured slightly different and will have different CSS (perhaps even different templating). My initial idea was to run them as separate applications with a common library but I have read about the sites framework which would allow them to run from a single instance of Django which may help to reduce memory usage. https://docs.djangoproject.com/en/dev/ref/contrib/sites/ Is the site framework the right approach to a problem like this, and does it have real benefits over running separate applications? Initially I thought it was, but now I think otherwise. I have heard the following: Your SITE_ID is set in settings.py, so in order to have multiple sites, you need multiple settings.py configurations, which means multiple distinct processes/instances. You can of course share the code base between them, but each site will need a dedicated worker / WSGIDaemon to serve the site. This effectively removes any benefit of running multiple sites under one hood, if each site needs a UWSGI instance running. Alternative ideas of systems: https://github.com/iivvoo/django_layers https://github.com/shestera/django-multisite I don't know what route to be taking with this.

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• How to convince management to deal with technical debt?

  - by Desolate Planet

  This is a question that I often ask myself when working with developers. I've worked at four companies so far, and I've noticed a lack of attention to keeping code clean and dealing with technical debt that hinders future progress in a software app. For example, the first company I worked for had written a database from scratch rather than take something like MySQL and that created hell for the team when refacoring or extending the app. I've always tried to be honest and clear with my manager when he discusses projections, but management doesn't seem interested in fixing what's already there and it's horrible to see the impact it has on team morale and in their attitude towards others. What are your thoughts on the best way to tackle this problem? What I've seen is people packing up and leaving and the company becomes a revolving door with developers coming and and out and making the code worse. How do you communicate this to management to get them interested in sorting out technical debt?

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• Need explanation of hexagonal architecture

  - by Victor Grazi

  I am reading about Alistair Cockburn's Hexagonal Architecture http://alistair.cockburn.us/Hexagonal+architecture with interest. One claim he makes is: "Finally, the automated function regression tests detect any violation of the promise to keep business logic out of the presentation layer. The organization can detect, and then correct, the logic leak." I do not understand this point. Is he saying that because the test is headless, then calls to a ui layer will throw exceptions? That doesn't seem to be a very sound test!

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• Is linq more efficient than it appears on the surface?

  - by Justin984

  If I write something like this: var things = mythings .Where(x => x.IsSomeValue) .Where(y => y.IsSomeOtherValue) Is this the same as: var results1 = new List<Thing>(); foreach(var t in mythings) if(t.IsSomeValue) results1.Add(t); var results2 = new List<Thing>(); foreach(var t in results1) if(t.IsSomeOtherValue) results2.Add(t); Or is there some magic under the covers that works more like this: var results = new List<Thing>(); foreach(var t in mythings) if(t.IsSomeValue && t.IsSomeOtherValue) results.Add(t); Or is it something completely different altogether?

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• What are the relative merits for implementing an Erlang-style "Continuation" pattern in C#

  - by JoeGeeky

  What are the relative merits (or demerits) for implementing an Erlang-style "Continuation" pattern in C#. I'm working on a project that has a large number of Lowest priority threads and I'm wondering if my approach may be all wrong. It would seem there is a reasonable upper limit to the number of long-running threads that any one Process 'should' spawn. With that said, I'm not sure what would signal the tipping-point for too many thread or when alternate patterns such as "Continuation" would be more suitable. In this case, many of the threads do a small amount of work and then sleep until woken to go again (Ex. Heartbeat, purge caches, etc...). This continues for the life of the Process.

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• Getting started with ClojureScript and Google Closure

  - by Andrea

  I would like to investigate whether ClojureScript, with the associated Google Closure library is a reasonable tool to build modern, in-browser, Javascript applications. My current Javascript stack consists of jQuery, Backbone and RequireJS with the possible additions of some widgets libraries like jQueryUI or KendoUI. So it will be quite a big leap (I already know how to work in Clojure, although I have little experience). What is a good roadmap to do so? Should I learn the Google Closure library first, or can I grasp it together with ClojureScript? One thing I am concerned about is the overall application structure. Backbone is rather opinionated on how to organize your application. I am not sure whether Google Closure also includes some components to help with the design of the application. And, if this is the case, I do not know how to tell whether this structure will port to ClojureScript or a ClojureScript application will require a different organization anyway, and only use - say - the widgets and DOM manipulation features of Closure.

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• How do I handle priority and propagation in an event system?

  - by Peeter

  Lets say I have a simple event system with the following syntax: object = new Object(); object.bind("my_trigger", function() { print "hello"; }); object.bind("my_trigger", function() { print "hello2"; }); object.trigger("my_trigger"); How could I make sure hello2 is printed out first (I do not want my code to depend on which order the events are binded). Ontop of that, how would I prevent my events from propagating (e.g. I want to stop every other event from being executed)

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• Good resources for language design

  - by Aaron Digulla

  There are lots of books about good web design, UI design, etc. With the advent of Xtext, it's very simple to write your own language. What are good books and resources about language design? I'm not looking for a book about compiler building (like the dragon book) but something that answers: How to create a grammar that is forgiving (like adding optional trailing commas)? Which grammar patterns cause problems for users of a language? How create a compact grammar without introducing ambiguities

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• Count unique visitors by group of visited places

  - by Mathieu

  I'm facing the problem of counting the unique visitors of groups of places. Here is the situation: I have visitors that can visit places. For example, that can be internet users visiting web pages, or customers going to restaurants. A visitor can visit as much places as he wishes, and a place can be visited by several visitors. A visitor can come to the same place several times. The places belong to groups. A group can obviously contain several places, and places can belong to several groups. Given that, for each visitor, we can have a list of visited places, how can I have the number of unique visitors per group of places? Example: I have visitors A, B, C and D; and I have places x, y and z. I have these visiting lists: [ A -> [x,x,y,x], B -> [], C -> [z,z], D -> [y,x,x,z] ] Having these number of unique visitors per place is quite easy: [ x -> 2, // A and D visited x y -> 2, // A and D visited y z -> 2 // C and D visited z ] But if I have these groups: [ G1 -> [x,y,z], G2 -> [x,z], G3 -> [x,y] ] How can I have this information? [ G1 -> 3, // A, C and D visited x or y or z G2 -> 3, // A, C and D visited x or z G3 -> 2 // A and D visited x or y ] Additional notes : There are so many places that it is not possible to store information about every possible group; It's not a problem if approximation are made. I don't need 100% precision. Having a fast algorithm that tells me that there were 12345 visits in a group instead of 12543 is better than a slow algorithm telling the exact number. Let's say there can be ~5% deviation. Is there an algorithm or class of algorithms that addresses this type of problem?

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• What's the best way to manage list item sort order with Drag & Drop UI?

  - by Reddy S R

  I have a list of Students that I should display to user on a web page in tabular format. The items are stored in DB along with SortOrder information. On the web page, user can rearrange the list order by dragging and dropping the items to their desired sort order, similar to this post. Below is a screenshot of my test page. In the above example, each row has sort order info attached to it. When I drop John Doe (Student Id 10) above the Student Id 1 row, the list order should now be: 2, 10, 1, 8, 11. What's the optimistic (less resource hungry) way to store and update Sort Order information? My only idea for now is, for every change in the list's sort order, every object's SortOrder value should be updated, which in my opinion is very resource hungry. Just FYI: I might have at most 25 rows in my table.

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• Design pattern for an automated mechanical test bench

  - by JJS

  Background I have a test fixture with a number of communication/data acquisition devices on it that is used as an end of line test for a product. Because of all the various sensors used in the bench and the need to run the test procedure in near real-time, I'm having a hard time structuring the program to be more friendly to modify later on. For example, a National Instruments USB data acquisition device is used to control an analog output (load) and monitor an analog input (current), a digital scale with a serial data interface measures position, an air pressure gauge with a different serial data interface, and the product is interfaced through a proprietary DLL that handles its own serial communication. The hard part The "real-time" aspect of the program is my biggest tripping point. For example, I need to time how long the product needs to go from position 0 to position 10,000 to the tenth of a second. While it's traveling, I need to ramp up an output of the NI DAQ when it reaches position 6,000 and ramp it down when it reaches position 8,000. This sort of control looks easy from browsing NI's LabVIEW docs but I'm stuck with C# for now. All external communication is done by polling which makes for lots of annoying loops. I've slapped together a loose Producer Consumer model where the Producer thread loops through reading the sensors and sets the outputs. The Consumer thread executes functions containing timed loops that poll the Producer for current data and execute movement commands as required. The UI thread polls both threads for updating some gauges indicating current test progress. Unsure where to start Is there a more appropriate pattern for this type of application? Are there any good resources for writing control loops in software (non-LabVIEW) that interface with external sensors and whatnot?

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• What happens at control invoke function?

  - by user65909

  A question about form controls invoke function. Control1 is created on thread1. If you want to update something in Control1 from thread2 you must do something like: delegate void SetTextCallback(string txt); void setText(string txt) { if (this.textBox1.InvokeRequired) { SetTextCallback d = new SetTextCallback(setText); this.Invoke(d, new object[] { txt }); } else { // this will run on thread1 even when called from thread2 this.textBox1.AppendText(msg); } }` What happens behind the scenes here? This invoke behaves different from a normal object invoke. When you want to call a function in an object on a specific thread, then that thread must be waiting on some queue of delegates, and execute the incoming delegates. Is it correct that the windows forms control invoke function is completely different from the standard object invoke function?

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• How should developers handle subpar working conditions? [closed]

  - by ivar

  I have been working in my current job for less than a year and at the beginning didn't have the courage to say anything about the things that bothered me. Now I'm a bit fed up and need things to get better. The first problem is not random but I'll mention it anyway. We are running out of space so every new employee gets a smaller table. We are promised that the space problem will be fixed soon. Almost every employee has a different keyboard, mouse, headphones (if any). Mine are $10 keyboard, some random cheap mouse and some random crappy headphones with a mic. All these were used and dirty when I got them. The number of monitor is 1-3 and with different sizes. I have 2 nice monitors and can't complain but some are given 1 small monitor. When it's their first job they don't have the guts to ask for 2 even if most others have 2. Nobody seems to care too. Project manager asked if it's ok? He obviously said he can handle the 1 small one. Then the manager said you can go ask for 1 more. I'm watching this and think go and ask where? The company is trying to hire more people but is not doing much after the person has signed the contract. We are put in one room that is open to the hallway and it's super noisy. Almost like a zoo at times. Even if nobody is talking the crappy keyboards make too much noise. Is this normal? Am I too negative and should I just do my job with what I was given? Should I demand better things? Should the company have some system that everybody gets things in some price range?

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