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  • What should every developer know about databases?

    - by Aaronaught
    Whether we like it or not, many if not most of us developers either regularly work with databases or may have to work with one someday. And considering the amount of misuse and abuse in the wild, and the volume of database-related questions that come up every day, it's fair to say that there are certain concepts that developers should know - even if they don't design or work with databases today. So: What are the important concepts that developers and other software professionals ought to know about databases? Guidelines for Responses: Keep your list short. One concept per answer is best. Be specific. "Data modelling" may be an important skill, but what does that mean precisely? Explain your rationale. Why is your concept important? Don't just say "use indexes." Don't fall into "best practices." Convince your audience to go learn more. Upvote answers you agree with. Read other people's answers first. One high-ranked answer is a more effective statement than two low-ranked ones. If you have more to add, either add a comment or reference the original. Don't downvote something just because it doesn't apply to you personally. We all work in different domains. The objective here is to provide direction for database novices to gain a well-founded, well-rounded understanding of database design and database-driven development, not to compete for the title of most-important.

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  • Which languages support *recursive* function literals / anonymous functions?

    - by Hugh Allen
    It seems quite a few mainstream languages support function literals these days. They are also called anonymous functions, but I don't care if they have a name. The important thing is that a function literal is an expression which yields a function which hasn't already been defined elsewhere, so for example in C, &printf doesn't count. EDIT to add: if you have a genuine function literal expression <exp>, you should be able to pass it to a function f(<exp>) or immediately apply it to an argument, ie. <exp>(5). I'm curious which languages let you write function literals which are recursive. Wikipedia's "anonymous recursion" article doesn't give any programming examples. Let's use the recursive factorial function as the example. Here are the ones I know: JavaScript / ECMAScript can do it with callee: function(n){if (n<2) {return 1;} else {return n * arguments.callee(n-1);}} it's easy in languages with letrec, eg Haskell (which calls it let): let fac x = if x<2 then 1 else fac (x-1) * x in fac and there are equivalents in Lisp and Scheme. Note that the binding of fac is local to the expression, so the whole expression is in fact an anonymous function. Are there any others?

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  • Is Polyglot programming important?

    - by Kb
    Trying to learn more about Polyglot programming. What is it exactly and is it important? Look like it is cross platform coding and interoperability across platforms... I found this article by Ted Neward (Thoughtworks) interesting.

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  • data structure algorithms for database searching

    - by Ygam
    I was used to the traditional way of doing database searching with the following using wildcards for term searches using where clause for specific data like addresses and names but at other times, I found these common methods to produce code that is so bloated, especially when it comes to complex searches. Are there algorithms out there that you use for complex database searching? I tried to look for some but had a hard time doing so. I stumbled accross the binary search but I can't find a use for it :(

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  • Is C# fast enough for games

    - by Matt
    Will a game written in C# have any speed issues after long periods of play, like for 24 hours at a time? I'm specifically talking about a 2D RPG similar to old Final Fantasy or Dragon Quest games. I know that languages like Python will slow down too much, curious how C# would stand.

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  • Is there an equivalent in Scala to Python's more general map function?

    - by wheaties
    I know that Scala's Lists have a map implementation with signature (f: (A) => B):List[B] and a foreach implementation with signature (f: (A) => Unit):Unit but I'm looking for something that accepts multiple iterables the same way that the Python map accepts multiple iterables. I'm looking for something with a signature of (f: (A,B) => C, Iterable[A], Iterable[B] ):Iterable[C] or equivalent. Is there a library where this exists or a comparable way of doing similar?

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  • What is the worst programming mistake you have made?

    - by George Edison
    Most of us are not perfect. (Well, except Jon Skeet) Have you made a terrible mistake that you would like to share? The idea is that we could all learn from our mistakes and by collecting them together here, we can avoid some common ones and discover some no-so-common ones we may have overlooked. Oh, and this question is CW, of course. Edit: This question is different than http://stackoverflow.com/questions/1928002/what-is-the-worst-programming-mistake-you-have-ever-seen because we are sharing our own mistakes. Edit again: And this one http://stackoverflow.com/questions/130965/what-is-the-worst-code-youve-ever-written is different too - it asks for code. My question does not have that restriction!

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  • Derivative of a Higher-Order Function

    - by Claudiu
    This is in the context of Automatic Differentiation - what would such a system do with a function like map, or filter - or even one of the SKI Combinators? Example: I have the following function: def func(x): return sum(map(lambda a: a**x, range(20))) What would its derivative be? What will an AD system yield as a result? (This function is well-defined on real-number inputs).

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  • Code Golf: Banknote calculator

    - by paxdiablo
    This question was posted by a C beginner and it was an exercise to calculate, given a dollar value input by the user, the minimum number of bills (or banknotes, depending on your locale) needed to reach that dollar value. So, if the user entered 93, the output would be: $20 bills = 4 $10 bills = 1 $5 bills = 0 $1 bills = 3 Finally succumbing to the phenomenon (it's a slow day here), I thought this would be ripe for a game of Code Golf. For fairness, the input prompt needs to be (note the "_" at the end is a space): Enter a dollar amount:_ I think I've covered all the bases: no identical question, community wiki. I won't be offended if it gets shut down though - of course, I'll never be able to complain about these types of questions again, for fear of being labelled a hypocrite :-) Okay, let's see what you can come up with. Here's a sample run: Enter a dollar amount: 127 $20 bills = 6 $10 bills = 0 $5 bills = 1 $1 bills = 2

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  • Are there any ASP.NET MVC subscription-based starter kits or examples?

    - by Wayne M
    Basically something that handles the low-level "plumbing" code for a subscription-based service. I see a lot of things dealing with basic membership, but nothing that handles the subscription aspect (recurring billing, automated jobs for setting up billing, notification for billing, etc). This might be the one thing that keeps me from using ASP.NET MVC for my SaaS idea, since it would take a fair amount of development time to write my own; if I go with my other option, Ruby on Rails, I can buy a kit that does all of this for $250. I haven't found anything even remotely close to this for .NET - all of the SaaS sample apps I've seen are more like StackOverflow et all where you have one site that multiple people log on to, not the web application model where you have subscribers who are billed monthly, each of whom has users and other entities (e.g. Customers, Tasks, etc) for their own site. Is there anything similar for ASP.NET, or some kind of guidelines for writing my own if I have to, so I don't waste too much time? As a startup that means that I'm doing all the coding myself. I've found this, but it seems to only be for billing and didn't seem to have much (any?) documentation on exactly how to set it up.

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  • Why scala not allowing '$' identifier in case statement?

    - by Alex R
    this works as expected scala 3 match { case x:Int = 2*x } res1: Int = 6 why does this fail? scala 3 match { case $x:Int = 2*$x } :1: error: '=' expected but ':' found. 3 match { case $x:Int = 2*$x } ^ scala 3 match { case `$x`:Int = 2*$x } :1: error: '=' expected but ':' found. 3 match { case `$x`:Int = 2*$x } ^ scala 3 match { case `$x` : Int = 2*$x } :1: error: '=' expected but ':' found. 3 match { case `$x` : Int = 2*$x } '$' is supposed to be a valid identifier character, as demonstrated here: scala var y = 1 y: Int = 1 scala var $y = 2 $y: Int = 2 Thanks

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  • Defend zero-based arrays

    - by DrJokepu
    A question asked here recently reminded me of a debate I had not long ago with a fellow programmer. Basically he argued that zero-based arrays should be replaced by one-based arrays since arrays being zero based is an implementation detail that originates from the way arrays and pointers and computer hardware work, but these sort of stuff should not be reflected in higher level languages. Now I am not really good at debating so I couldn't really offer any good reasons to stick with zero-based arrays other than they sort of feel like more appropriate. I am really interested in the opinions of other developers, so I sort of challenge you to come up with reasons to stick with zero-based arrays!

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  • How to find two most distant points?

    - by depesz
    This is a question that I was asked on a job interview some time ago. And I still can't figure out sensible answer. Question is: you are given set of points (x,y). Find 2 most distant points. Distant from each other. For example, for points: (0,0), (1,1), (-8, 5) - the most distant are: (1,1) and (-8,5) because the distance between them is larger from both (0,0)-(1,1) and (0,0)-(-8,5). The obvious approach is to calculate all distances between all points, and find maximum. The problem is that it is O(n^2), which makes it prohibitively expensive for large datasets. There is approach with first tracking points that are on the boundary, and then calculating distances for them, on the premise that there will be less points on boundary than "inside", but it's still expensive, and will fail in worst case scenario. Tried to search the web, but didn't find any sensible answer - although this might be simply my lack of search skills.

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  • Multithreading and Interrupts

    - by Nicholas Flynt
    I'm doing some work on the input buffers for my kernel, and I had some questions. On Dual Core machines, I know that more than one "process" can be running simultaneously. What I don't know is how the OS and the individual programs work to protect collisions in data. There are two things I'd like to know on this topic: (1) Where do interrupts occur? Are they guaranteed to occur on one core and not the other, and could this be used to make sure that real-time operations on one core were not interrupted by, say, file IO which could be handled on the other core? (I'd logically assume that the interrupts would happen on the 1st core, but is that always true, and how would you tell? Or perhaps does each core have its own settings for interrupts? Wouldn't that lead to a scenario where each core could react simultaneously to the same interrupt, possibly in different ways?) (2) How does the dual core processor handle opcode memory collision? If one core is reading an address in memory at exactly the same time that another core is writing to that same address in memory, what happens? Is an exception thrown, or is a value read? (I'd assume the write would work either way.) If a value is read, is it guaranteed to be either the old or new value at the time of the collision? I understand that programs should ideally be written to avoid these kinds of complications, but the OS certainly can't expect that, and will need to be able to handle such events without choking on itself.

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  • ildasm and dynamic exe files

    - by TonyNeallon
    Hi There, I am trying to create an application can modify properties in IL to create a slightly different executable. E.g Client A runs app and a label on the WinForm label Reads "Client A:". Client B runs the app and Label Says "Client B". Easy I know using config files or resource files but thats not an option for this project. The Main program needs to be able to generate .exe file dynamically based on some form fields entered by user. My solution was to create a standalone executable that contained all the elements which I needed to make dynamic. I then used ildasm to generate the IL and thought that I could use this IL and substitute tags for the elements i wanted to make dynamic. I could then replace those tags at runtime after user filled the form using regex etc. The problem is, the if i re save the IL file generated by ILDASM as an exe and try to run it. I just launches console and does nothing. Am I going about this the wrong way? I didnt want to delve into Reflection as the dynamic .exe is a really simple one and I thought reverse engineering IL with ildasm would be the quickest way. You thoughts and pointers are much appreciated. Tony

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  • What was "The Next Big Thing" when you were just starting out in programming?

    - by Andrew
    I'm at the beginning of my career and there are lots of things which are being touted as "The Next Big Thing". For example: Dependency Injection (Spring, etc) MVC (Struts, ASP.NET MVC) ORMs (Linq To SQL, Hibernate) Agile Software Development These things have probably been around for some time, but I've only just started out. And don't get me wrong, I think these things are great! So, what was "The Next Big Thing" when you were starting out? When was it? Were people sceptical of it at first? Why? Did you think it would catch on? Did it pan out and become widely accepted/used? If not, why not? EDIT It's been nearly a week since I first posted this question and I can safely say that I did not expect such explosive interest. I asked the question so that I could gain a perspective of what kinds of innovations in programming people thought were most important when they were starting out. At the time of writing this I have read ~95% of all answers. To answer a few questions, the "Next Big Things" I listed are ones that I am currently really excited about and that I had not really been exposed to until I started working. I'm hoping to implement some or all of these in the near future at my current workplace. To many people they are probably old news. In regards to the "is this a real question" debate, I can see that obviously hasn't been settled yet. I feel bad whenever I read a comment saying that these kinds of questions take away from the real meaning of SO. I'm not wholly convinced that it doesn't. On the other hand, I have seen a lot of comments saying what a great question it is. Anyway, I have chosen "The Internet!" as my answer to this question. I don't think (in my very humble opinion, and, it seems many SOers opinions) that many things related to programming can compare. Nowadays every business and their dog has a website which can do anything from simply supplying information to purchasing goods halfway around the world to updating your blog. And of course, all these businesses need people like us. Thanks to everyone for all the great answers!

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  • Is it immoral to write crappy code even if readability and correctness is not a requirement?

    - by mafutrct
    There are cases when crappy (i.e. unreadable and buggy) code is not much of a problem. For instance, imagine you need to generate a big text file that mostly follows a simple pattern with a few very complex exceptions. What do you do? You quickly write a simple algorithm and insert the exceptional bits in the output manually to save 4 hours. The code is unreadable, and the output is flawed, but it's still the correct way since it is way faster. But let's get this straight: I hate bad code. I've had to read and work with code that caused my stomach to hurt. I care a lot about good code. And actually, I caught myself thinking that it is immoral to write bad code even though the dirty approach is sometimes superior. I was surprised by myself and found my idea to be very irrational. Did you ever experience this? Should I just get rid of this stupid idea and use the most efficient approach to coding?

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  • Business Objects - Containers or functional?

    - by Walter
    Where I work, we've gone back and forth on this subject a number of times and are looking for a sanity check. Here's the question: Should Business Objects be data containers (more like DTOs) or should they also contain logic that can perform some functionality on that object. Example - Take a customer object, it probably contains some common properties (Name, Id, etc), should that customer object also include functions (Save, Calc, etc.)? One line of reasoning says separate the object from the functionality (single responsibility principal) and put the functionality in a Business Logic layer or object. The other line of reasoning says, no, if I have a customer object I just want to call Customer.Save and be done with it. Why do I need to know about how to save a customer if I'm consuming the object? Our last two projects have had the objects separated from the functionality, but the debate has been raised again on a new project. Which makes more sense? EDIT These results are very similar to our debates. One vote to one side or another completely changes the direction. Does anyone else want to add their 2 cents? EDIT Eventhough the answer sampling is small, it appears that the majority believe that functionality in a business object is acceptable as long as it is simple but persistence is best placed in a separate class/layer. We'll give this a try. Thanks for everyone's input...

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