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  • Programming With Markov Algorithms.

    - by Bubba88
    Hello! I Wonder if someone has used Markov Algorithm-based programming system or embedded facility in production or for scientific purpose. I know about 'REFAL' programming language invented a thousand years ago, but it all seems to be dead, so.. Ref: http://en.wikipedia.org/wiki/Markov_algorithm

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  • Canonical pattern reference in Actors programming model.

    - by Bubba88
    Hello! Is there a source, which I could use to learn some of the most used and popular practices regarding Actor-/Agent-oriented programming. My primary concern is about parallelism and distribution limited to the mentioned scheme - Actors, message passing. Should I begin with Erlang documentation or maybe there is any kind of book that describes the most important building blocks when programming Actor-oriented? Thank you! (Most useful examples would be in Scala or F#)

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  • Any learning/studying material for C/C++ that use game programming as learning context out there?

    - by mac
    As most of game programming is done - I read on this very site - in C/C++ I was wondering if there is any learning/studying material for C/C++ that would target specifically game programming. I am not looking for material about "developing games" or "software architecture for games", but rather for material that uses "game programming" as the CONTEXT for introducing and illustrating C/C++ features, idioms, programming techniques, etc... With a simile: think to the GOF book on design patterns. There, they used "developing a text-editor" as a context for introducing design patterns, but the book is most definitively not a book about "developing text-editors". Thanks in advance for your time and advice! PS: My background: I am a programmer with a solid experience in OO scripting languages and only some experience in C and Assembler (on AVR microcontrollers), so I am thinking to mid-to-advanced level material, rather than tutorials for beginners, although it might be interesting to take a look to the latter ones if nothing else is available.

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  • How can I know if programming is right for me?

    - by user66414
    I have an IT background and was pretty confident until an opportunity came up at work to go into programming(C#). I have never programmed before this, and the software I am programming for is a program I have never used before (a 3D modeling software). It has been 6 months since then and I feel like giving up. I didn't get much training... about 3 weeks of training spread out over the last 6 months. I think I would be good at programming but this experience is kinda making me rethink my decision. I'm not sure if it's just me, or if this frustration is normal. How can I tell if programming is right for me?

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  • Where to start game programming for Android

    - by Marthin
    Hi, I'm new to game programming. But I'v got an ide for what I think would be a fun game for the Android platform. My question is, where do I start? Anyone got some good sites to recommend or perhaps a book or two. I'v got medium skills when it come to programming but i'v got a masters of science degree in computer engineering so i'm not totally unfamiliar with algorithms and stuff. Thx for any help! /Marthin

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  • Will Beej's Guide to Network programming point me the right way to be able to make multiplayer games and a web broswer?

    - by Logan545
    I'm new to socket programming in C, and I've found the Beej's Guide to Networking programming. It looks fine and all, however, I just wanted to ask whether this tutorial will point me in the right direction in terms of network programming. I plan to build a game in opengl that will be multiplayer using c+ and possibly a web browser. I know this tutorial would by no means teach me how to do this, but would this be a good way to start off on my path?

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  • How do I transition from physics and math to programming?

    - by inovaovao
    I'm a physics PhD with little actual programming experience. I've always liked programming and played around with BASIC, Pascal as a teen, but the extent of my experience writing complex programs comes from an introductory course in computer science. Now I've decided that I'm more interested in programming than in physics and started to learn Java. Coming from a physics or math-heavy background, what would be the best strategy to maximize my value in the field?

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  • Alternative languages for embedded programming

    - by RHaguiuda
    I`m looking for alternatives programming languages (from assembly, C, C++ and basic) to embedded (microcontroller) programming. Is it possible for example, to programm microcontrollers in C# or Java? Maybe Ruby or Phyton? If possible, please post development tools and hardware used. Thanks

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  • MapReduce programming system in java-actionscript

    - by eco_bach
    Just finished reading ch23 in the excellent 'Beautiful Code' http://oreilly.com/catalog/9780596510046 on Distributed Programming with MapReduce. I understand that MapReduce is a programming system designed for large-scale data processing problems, but I have a hard time getting my head around the basic examples given and how I might apply them in real world situations. Can someone give a simple example of MapReduce implemented using either java, javascript or actionscript?

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  • How to stay connected to the programming community?

    - by Anton
    I often find myself detached from the programming community and I generally find out about all the "cool" things that are happening after they have already happened. So my question is how do you stay connected and up to date with the programming community? Podcasts, blogs, meet ups, conventions, twitter, talking with your co-workers whatever it may be that keeps you connected. Please provide actual examples of which blogs, talks, etc you use.

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  • Best programming language for teaching econometrics?

    - by TJB
    I will be teaching an econometrics course to masters students in the fall. I think it is important for them to learn programming with data as an essential applied research skill. What suggestions do you have for the programming language. I am leaning mostly towards R. What others should I consider?

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  • GUI programming, what to learn, already know console C++

    - by conqrr
    i have already learnt c++ console(love it!) and want to do gui programming, i have looked at Qt but i dont like the size of exe produced at all,even after compressing or static linking.... Shall i learn c# and gui programming?? is it easy to move from c++? what is dot net exactly by the way and how can it be useful to me and my CV in future??

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  • Website programming language [closed]

    - by Develman
    Hello everybody, I have worked a lot with PHP in last times, but I am not sure if it is the best choice for website programming. What language do you prefer for website programming? Which type (private, business, etc.) of website do you build with that language?

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  • How important is self-teaching in the programming field? [closed]

    - by ThePlan
    I'm 16. I started programming about a year ago when I was about to start high-school. I'm going for a career in programming, and I'm doing my best to learn as much as I can. When I first started, I learned the basics of C++ from a book and I started to learn things by myself from there on. Nowadays I'm much more experienced than I was a year ago. I knew I had to study by myself because high-school won't (likely) teach me anything valuable about programming, and I want to be prepared. The question here is: how important is it to study programming by oneself?

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  • When did you feel comfortable with programming?

    - by misterwebz
    I've been programming for about 6 months, but i still feel like i haven't learned anything. Or maybe i'm overwhelmed by the things i still don't know. Am i doing something wrong here or is this normal? I want to be able to work as a freelancer in a year or two, but i'm not sure if that goal is achievable. So when did you feel comfortable using your programming language of choice and how did you learn it?

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  • Use the right tool for the job: embedded programming

    - by EmbeddedProg
    I'm interested in programming languages well suited for embedded programming. In particular: Is it possible to program embedded systems in C++? Or is it better to use pure C? Or is C++ OK only if some features of the language (e.g. RTTI, exceptions and templates) are excluded? What about Java in this domain? Thanks.

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  • How can I figure out if programming is right for me? [closed]

    - by user66414
    I have an IT background and was pretty confident until an opportunity came up at work to go into programming(C#). I have never programmed before this, and the software I am programming for is a program I have never used before (a 3D modeling software). It has been 6 months since then and I feel like giving up. I didn't get much training... about 3 weeks of training spread out over the last 6 months. I think I would be good at programming but this experience is kinda making me rethink my decision. I'm not sure if it's just me, or if this frustration is normal. How can I tell if programming is right for me?

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  • Project manager programming background

    - by Henryk Konsek
    Do you think that project manager should have programming background? Do you consider this role as a natural way of evolution for the skilled/leader programmers (as an alternative for architect role)? Or maybe you believe that PM should be just a good manager with a basic understanding of the programming concepts and a fundamental knowledge about the technology you use. What is your experience with working with both kinds of managers (ex-programmers or just managers).

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  • Design by Contract with Microsoft .Net Code Contract

    - by Fredrik N
    I have done some talks on different events and summits about Defensive Programming and Design by Contract, last time was at Cornerstone’s Developer Summit 2010. Next time will be at SweNug (Sweden .Net User Group). I decided to write a blog post about of some stuffs I was talking about. Users are a terrible thing! Protect your self from them ”Human users have a gift for doing the worst possible thing at the worst possible time.” – Michael T. Nygard, Release It! The kind of users Michael T. Nygard are talking about is the users of a system. We also have users that uses our code, the users I’m going to focus on is the users of our code. Me and you and another developers. “Any fool can write code that a computer can understand. Good programmers write code that humans can understand.” – Martin Fowler Good programmers also writes code that humans know how to use, good programmers also make sure software behave in a predictable manner despise inputs or user actions. Design by Contract   Design by Contract (DbC) is a way for us to make a contract between us (the code writer) and the users of our code. It’s about “If you give me this, I promise to give you this”. It’s not about business validations, that is something completely different that should be part of the domain model. DbC is to make sure the users of our code uses it in a correct way, and that we can rely on the contract and write code in a way where we know that the users will follow the contract. It will make it much easier for us to write code with a contract specified. Something like the following code is something we may see often: public void DoSomething(Object value) { value.DoIKnowThatICanDoThis(); } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } Where “value” can be uses directly or passed to other methods and later be used. What some of us can easily forget here is that the “value” can be “null”. We will probably not passing a null value, but someone else that uses our code maybe will do it. I think most of you (including me) have passed “null” into a method because you don’t know if the argument need to be specified to a valid value etc. I bet most of you also have got the “Null reference exception”. Sometimes this “Null reference exception” can be hard and take time to fix, because we need to search among our code to see where the “null” value was passed in etc. Wouldn’t it be much better if we can as early as possible specify that the value can’t not be null, so the users of our code also know it when the users starts to use our code, and before run time execution of the code? This is where DbC comes into the picture. We can use DbC to specify what we need, and by doing so we can rely on the contract when we write our code. So the code above can actually use the DoIKnowThatICanDoThis() method on the value object without being worried that the “value” can be null. The contract between the users of the code and us writing the code, says that the “value” can’t be null.   Pre- and Postconditions   When working with DbC we are specifying pre- and postconditions.  Precondition is a condition that should be met before a query or command is executed. An example of a precondition is: “The Value argument of the method can’t be null”, and we make sure the “value” isn’t null before the method is called. Postcondition is a condition that should be met when a command or query is completed, a postcondition will make sure the result is correct. An example of a postconditon is “The method will return a list with at least 1 item”. Commands an Quires When using DbC, we need to know what a Command and a Query is, because some principles that can be good to follow are based on commands and queries. A Command is something that will not return anything, like the SQL’s CREATE, UPDATE and DELETE. There are two kinds of Commands when using DbC, the Creation commands (for example a Constructor), and Others. Others can for example be a Command to add a value to a list, remove or update a value etc. //Creation commands public Stack(int size) //Other commands public void Push(object value); public void Remove(); .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   A Query, is something that will return something, for example an Attribute, Property or a Function, like the SQL’s SELECT.   There are two kinds of Queries, the Basic Queries  (Quires that aren’t based on another queries), and the Derived Queries, queries that is based on another queries. Here is an example of queries of a Stack: //Basic Queries public int Count; public object this[int index] { get; } //Derived Queries //Is related to Count Query public bool IsEmpty() { return Count == 0; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } To understand about some principles that are good to follow when using DbC, we need to know about the Commands and different Queries. The 6 Principles When working with DbC, it’s advisable to follow some principles to make it easier to define and use contracts. The following DbC principles are: Separate commands and queries. Separate basic queries from derived queries. For each derived query, write a postcondition that specifies what result will be returned, in terms of one or more basic queries. For each command, write a postcondition that specifies the value of every basic query. For every query and command, decide on a suitable precondition. Write invariants to define unchanging properties of objects. Before I will write about each of them I want you to now that I’m going to use .Net 4.0 Code Contract. I will in the rest of the post uses a simple Stack (Yes I know, .Net already have a Stack class) to give you the basic understanding about using DbC. A Stack is a data structure where the first item in, will be the first item out. Here is a basic implementation of a Stack where not contract is specified yet: public class Stack { private object[] _array; //Basic Queries public uint Count; public object this[uint index] { get { return _array[index]; } set { _array[index] = value; } } //Derived Queries //Is related to Count Query public bool IsEmpty() { return Count == 0; } //Is related to Count and this[] Query public object Top() { return this[Count]; } //Creation commands public Stack(uint size) { Count = 0; _array = new object[size]; } //Other commands public void Push(object value) { this[++Count] = value; } public void Remove() { this[Count] = null; Count--; } } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   Note: The Stack is implemented in a way to demonstrate the use of Code Contract in a simple way, the implementation may not look like how you would implement it, so don’t think this is the perfect Stack implementation, only used for demonstration.   Before I will go deeper into the principles I will simply mention how we can use the .Net Code Contract. I mention before about pre- and postcondition, is about “Require” something and to “Ensure” something. When using Code Contract, we will use a static class called “Contract” and is located in he “System.Diagnostics.Contracts” namespace. The contract must be specified at the top or our member statement block. To specify a precondition with Code Contract we uses the Contract.Requires method, and to specify a postcondition, we uses the Contract.Ensure method. Here is an example where both a pre- and postcondition are used: public object Top() { Contract.Requires(Count > 0, "Stack is empty"); Contract.Ensures(Contract.Result<object>() == this[Count]); return this[Count]; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   The contract above requires that the Count is greater than 0, if not we can’t get the item at the Top of a Stack. We also Ensures that the results (By using the Contract.Result method, we can specify a postcondition that will check if the value returned from a method is correct) of the Top query is equal to this[Count].   1. Separate Commands and Queries   When working with DbC, it’s important to separate Command and Quires. A method should either be a command that performs an Action, or returning information to the caller, not both. By asking a question the answer shouldn’t be changed. The following is an example of a Command and a Query of a Stack: public void Push(object value) public object Top() .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   The Push is a command and will not return anything, just add a value to the Stack, the Top is a query to get the item at the top of the stack.   2. Separate basic queries from derived queries There are two different kinds of queries,  the basic queries that doesn’t rely on another queries, and derived queries that uses a basic query. The “Separate basic queries from derived queries” principle is about about that derived queries can be specified in terms of basic queries. So this principles is more about recognizing that a query is a derived query or a basic query. It will then make is much easier to follow the other principles. The following code shows a basic query and a derived query: //Basic Queries public uint Count; //Derived Queries //Is related to Count Query public bool IsEmpty() { return Count == 0; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   We can see that IsEmpty will use the Count query, and that makes the IsEmpty a Derived query.   3. For each derived query, write a postcondition that specifies what result will be returned, in terms of one or more basic queries.   When the derived query is recognize we can follow the 3ed principle. For each derived query, we can create a postcondition that specifies what result our derived query will return in terms of one or more basic queries. Remember that DbC is about contracts between the users of the code and us writing the code. So we can’t use demand that the users will pass in a valid value, we must also ensure that we will give the users what the users wants, when the user is following our contract. The IsEmpty query of the Stack will use a Count query and that will make the IsEmpty a Derived query, so we should now write a postcondition that specified what results will be returned, in terms of using a basic query and in this case the Count query, //Basic Queries public uint Count; //Derived Queries public bool IsEmpty() { Contract.Ensures(Contract.Result<bool>() == (Count == 0)); return Count == 0; } The Contract.Ensures is used to create a postcondition. The above code will make sure that the results of the IsEmpty (by using the Contract.Result to get the result of the IsEmpty method) is correct, that will say that the IsEmpty will be either true or false based on Count is equal to 0 or not. The postcondition are using a basic query, so the IsEmpty is now following the 3ed principle. We also have another Derived Query, the Top query, it will also need a postcondition and it uses all basic queries. The Result of the Top method must be the same value as the this[] query returns. //Basic Queries public uint Count; public object this[uint index] { get { return _array[index]; } set { _array[index] = value; } } //Derived Queries //Is related to Count and this[] Query public object Top() { Contract.Ensures(Contract.Result<object>() == this[Count]); return this[Count]; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   4. For each command, write a postcondition that specifies the value of every basic query.   For each command we will create a postconditon that specifies the value of basic queries. If we look at the Stack implementation we will have three Commands, one Creation command, the Constructor, and two others commands, Push and Remove. Those commands need a postcondition and they should include basic query to follow the 4th principle. //Creation commands public Stack(uint size) { Contract.Ensures(Count == 0); Count = 0; _array = new object[size]; } //Other commands public void Push(object value) { Contract.Ensures(Count == Contract.OldValue<uint>(Count) + 1); Contract.Ensures(this[Count] == value); this[++Count] = value; } public void Remove() { Contract.Ensures(Count == Contract.OldValue<uint>(Count) - 1); this[Count] = null; Count--; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   As you can see the Create command will Ensures that Count will be 0 when the Stack is created, when a Stack is created there shouldn’t be any items in the stack. The Push command will take a value and put it into the Stack, when an item is pushed into the Stack, the Count need to be increased to know the number of items added to the Stack, and we must also make sure the item is really added to the Stack. The postconditon of the Push method will make sure the that old value of the Count (by using the Contract.OldValue we can get the value a Query has before the method is called)  plus 1 will be equal to the Count query, this is the way we can ensure that the Push will increase the Count with one. We also make sure the this[] query will now contain the item we pushed into the Stack. The Remove method must make sure the Count is decreased by one when the top item is removed from the Stack. The Commands is now following the 4th principle, where each command now have a postcondition that used the value of basic queries. Note: The principle says every basic Query, the Remove only used one Query the Count, it’s because this command can’t use the this[] query because an item is removed, so the only way to make sure an item is removed is to just use the Count query, so the Remove will still follow the principle.   5. For every query and command, decide on a suitable precondition.   We have now focused only on postcondition, now time for some preconditons. The 5th principle is about deciding a suitable preconditon for every query and command. If we starts to look at one of our basic queries (will not go through all Queries and commands here, just some of them) the this[] query, we can’t pass an index that is lower then 1 (.Net arrays and list are zero based, but not the stack in this blog post ;)) and the index can’t be lesser than the number of items in the stack. So here we will need a preconditon. public object this[uint index] { get { Contract.Requires(index >= 1); Contract.Requires(index <= Count); return _array[index]; } } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } Think about the Contract as an documentation about how to use the code in a correct way, so if the contract could be specified elsewhere (not part of the method body), we could simply write “return _array[index]” and there is no need to check if index is greater or lesser than Count, because that is specified in a “contract”. The implementation of Code Contract, requires that the contract is specified in the code. As a developer I would rather have this contract elsewhere (Like Spec#) or implemented in a way Eiffel uses it as part of the language. Now when we have looked at one Query, we can also look at one command, the Remove command (You can see the whole implementation of the Stack at the end of this blog post, where precondition is added to more queries and commands then what I’m going to show in this section). We can only Remove an item if the Count is greater than 0. So we can write a precondition that will require that Count must be greater than 0. public void Remove() { Contract.Requires(Count > 0); Contract.Ensures(Count == Contract.OldValue<uint>(Count) - 1); this[Count] = null; Count--; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   6. Write invariants to define unchanging properties of objects.   The last principle is about making sure the object are feeling great! This is done by using invariants. When using Code Contract we can specify invariants by adding a method with the attribute ContractInvariantMethod, the method must be private or public and can only contains calls to Contract.Invariant. To make sure the Stack feels great, the Stack must have 0 or more items, the Count can’t never be a negative value to make sure each command and queries can be used of the Stack. Here is our invariant for the Stack object: [ContractInvariantMethod] private void ObjectInvariant() { Contract.Invariant(Count >= 0); } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   Note: The ObjectInvariant method will be called every time after a Query or Commands is called. Here is the full example using Code Contract:   public class Stack { private object[] _array; //Basic Queries public uint Count; public object this[uint index] { get { Contract.Requires(index >= 1); Contract.Requires(index <= Count); return _array[index]; } set { Contract.Requires(index >= 1); Contract.Requires(index <= Count); _array[index] = value; } } //Derived Queries //Is related to Count Query public bool IsEmpty() { Contract.Ensures(Contract.Result<bool>() == (Count == 0)); return Count == 0; } //Is related to Count and this[] Query public object Top() { Contract.Requires(Count > 0, "Stack is empty"); Contract.Ensures(Contract.Result<object>() == this[Count]); return this[Count]; } //Creation commands public Stack(uint size) { Contract.Requires(size > 0); Contract.Ensures(Count == 0); Count = 0; _array = new object[size]; } //Other commands public void Push(object value) { Contract.Requires(value != null); Contract.Ensures(Count == Contract.OldValue<uint>(Count) + 1); Contract.Ensures(this[Count] == value); this[++Count] = value; } public void Remove() { Contract.Requires(Count > 0); Contract.Ensures(Count == Contract.OldValue<uint>(Count) - 1); this[Count] = null; Count--; } [ContractInvariantMethod] private void ObjectInvariant() { Contract.Invariant(Count >= 0); } } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } Summary By using Design By Contract we can make sure the users are using our code in a correct way, and we must also make sure the users will get the expected results when they uses our code. This can be done by specifying contracts. To make it easy to use Design By Contract, some principles may be good to follow like the separation of commands an queries. With .Net 4.0 we can use the Code Contract feature to specify contracts.

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  • Recommended programming language for linux server management and web ui integration

    - by Brendan Martens
    I am interested in making an in house web ui to ease some of the management tasks I face with administrating many servers; think Canonical's Landscape. This means doing things like, applying package updates simultaneously across servers, perhaps installing a custom .deb (I use ubuntu/debian.) Reviewing server logs, executing custom scripts, viewing status information for all my servers. I hope to be able to reuse existing command line tools instead of rewriting the exact same operations in a different language myself. I really want to develop something that allows me to continue managing on the ssh level but offers the power of a web interface for easily applying the same infrastructure wide changes. They should not be mutually exclusive. What are some recommended programming languages to use for doing this kind of development and tying it into a web ui? Why do you recommend the language(s) you do? I am not an experienced programmer, but view this as an opportunity to scratch some of my own itches as well as become a better programmer. I do not care specifically if one language is harder than another, but am more interested in picking the best tools for the job from the beginning. Feel free to recommend any existing projects that already integrate management of many systems into a single cohesive web ui, except Landscape (not free,) Ebox (ebox control center not free) and webmin (I don't like it, feels clunky and does not integrate well with the "debian way" of maintaining a server, imo. Also, only manages one system.) Thanks for any ideas! Update: I am not looking to reinvent the wheel of systems management, I just want to "glue" many preexisting and excellent tools together where possible and appropriate; this is why I wonder about what languages can interact well with pre-existing command line tools, while making them manageable with a web ui.

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  • Does fast typing influence fast programming?

    - by Lukasz Lew
    Many young programmers think that their bottleneck is typing speed. After some experience one realizes that it is not the case, you have to think much more than type. At some point my room-mate forced me to turn of the light (he sleeps during the night). I had to learn to touch type and I experienced an actual improvement in programming skill. The most surprising was that the improvement not due to sheer typing speed, but to a change in mindset. I'm less afraid now to try new things and refactor them later if they work well. It's like having a new tool in the bag. Have anyone of you had similar experience? Now I trained a touch typing a little with KTouch. I find auto-generate lessons the best. I can use this program to create new lessons out of text files but it's only verbatim training, not auto-generated based on a language model. Do you know any touch typing program that allows creation of custom, but randomized lessons?

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  • Pair programming with tmux and Vagrant

    - by neezer
    Does anyone have a clear step-by-step guide for setting up a shared tmux session on a Vagrant vbox that my coworkers (on our local office lan) could SSH into? The articles I've found online only seem to cover setting this up from machine to machine (no virtualbox setups), and I'm not very good at networking, so I haven't been able to extrapolate a solution... We're all running the latest Macs in our office, btw. Here's one article I've found but haven't been able to get working with Vagrant: http://blog.voxdolo.me/remote-pairing-with-vim-and-tmux.html EDIT: To clarify, I don't really know how I should be setting up Vagrant to allow me to SSH into it from a machine outside the one hosting the VM. The article above suggests that I add the tunnels host on my physical machine running the VM (here-on referred to as the MBP), so I did that. Next is the ProxyCommand host declaration, which I have also assumed should live on the MBP. So next I try SSHing into the MBP from a guest machine (another separate physical machine on my network), and that seems to work... but that only gets me into the MBP, not the Vagrant image running on the MBP. I normally login Vagrant image on the MBP via vagrant ssh (per the docs), and I know how to forward ports on the Vagrant VM to the MBP, but it's unclear to me how I could forward ports/SSH from the MBP to the Vagrant VM, which I assume I would need to do so that my guest machine could SSH in--through the MBP--to my Vagrant image. That, in a nutshell, is what I'm trying to accomplish. I do my development work in Vagrant VMs which keeps my MBP nice and clean of any dev-related cruft and also keeps my dev environments totally isolated from one another, yet I would like to start pair-programming with my coworkers via tmux, thus the reason why I've asked this question. I would like to accomplish all of this without setting up an additional user account on the MBP, or giving my coworkers access to my local user account on the MBP to get to my Vagrant VM, if that's at all possible.

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