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• What are C/C++ specific idioms?

  - by Ole Jak

  thay say A good C/C++ programmer should be familiar with language idioms that typically do not exist for ex in Java. What are such idioms?

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• Common Ruby Idioms

  - by DanSingerman

  One thing I love about ruby is that mostly it is a very readable language (which is great for self-documenting code) However, inspired by this question: http://stackoverflow.com/questions/609612/ruby-code-explained and the description of how ||= works in ruby, I was thinking about the ruby idioms I don't use, as frankly, I don't fully grok them. So my question is, similar to the example from the referenced question, what common, but not obvious, ruby idioms do I need to be aware of to be a truly proficient ruby programmer? By the way, from the referenced question a ||= b is equivalent to if a == nil || a == false a = b end (Thanks to Ian Terrell for the correction) Edit: It turns out this point is not totally uncontroversial. The correct expansion is in fact (a || (a = (b))) See these links for why: http://DABlog.RubyPAL.Com/2008/3/25/a-short-circuit-edge-case/ http://DABlog.RubyPAL.Com/2008/3/26/short-circuit-post-correction/ http://ProcNew.Com/ruby-short-circuit-edge-case-response.html Thanks to Jörg W Mittag for pointing this out.

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• x86 assembly idioms

  - by susmits

  I've been trying to get a good hold on the x86 assembly language, and was wondering if there was a quick-and-short equivalent of movl $1, %eax. That's when I thought that a list of idioms used frequently in the language would perhaps be a good idea. This could include the preferred use of xorl %eax, %eax as opposed to movl $0, %eax, or testl %eax, %eax against cmpl $0, %eax. Oh, and kindly post one example per post!

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• idioms for returning multiple values in shell scripting

  - by Wang

  Are there any idioms for returning multiple values from a bash function within a script? http://tldp.org/LDP/abs/html/assortedtips.html describes how to echo multiple values and process the results (e.g., example 35-17), but that gets tricky if some of the returned values are strings with spaces in. A more structured way to return would be to assign to global variables, like foo () { FOO_RV1="bob" FOO_RV2="bill" } foo echo "foo returned ${FOO_RV1} and ${FOO_RV2}" I realize that if I need re-entrancy in a shell script I'm probably doing it wrong, but I still feel very uncomfortable throwing global variables around just to hold return values. Is there a better way? I would prefer portability, but it's probably not a real limitation if I have to specify #!/bin/bash.

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• How to program for constraints/rules

  - by Gaurav

  First the background, during interviews in the past, many times I have been asked to design some or other variation of card game as programming puzzle, and I have tried to design it in OO way, but I have never been satisfied with my solutions. However it was not until recently that I realized that I had been approaching the problem from the wrong direction. Specifically I was trying to solve the problem by modeling individual card as an object. Problem with this is individual cards don't have any non-trivial intrinsic behavior and therefore are not suitable (or primary) candidate as objects. What is interesting and important about cards are rules and constraints, such as there could be only four suits, or only thirteen cards in each suit. Of course, then there are any number of rules for games. So my questions are Are there any idioms/constructs/patterns to program for rules & constraints. How many in 1 can be applied in conjunction with OO paradigm.

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• Which programming idiom to choose for this open source library?

  - by Walkman

  I have an interesting question about which programming idiom is easier to use for beginner developers writing concrete file parsing classes. I'm developing an open source library, which one of the main functionality is to parse plain text files and get structured information from them. All of the files contains the same kind of information, but can be in different formats like XML, plain text (each of them is structured differently), etc. There are a common set of information pieces which is the same in all (e.g. player names, table names, some id numbers) There are formats which are very similar to each other, so it's possible to define a common Base class for them to facilitate concrete format parser implementations. So I can clearly define base classes like SplittablePlainTextFormat, XMLFormat, SeparateSummaryFormat, etc. Each of them hints the kind of structure they aim to parse. All of the concrete classes should have the same information pieces, no matter what. To be useful at all, this library needs to define at least 30-40 of these parsers. A couple of them are more important than others (obviously the more popular formats). Now my question is, which is the best programming idiom to choose to facilitate the development of these concrete classes? Let me explain: I think imperative programming is easy to follow even for beginners, because the flow is fixed, the statements just come one after another. Right now, I have this: class SplittableBaseFormat: def parse(self): "Parses the body of the hand history, but first parse header if not yet parsed." if not self.header_parsed: self.parse_header() self._parse_table() self._parse_players() self._parse_button() self._parse_hero() self._parse_preflop() self._parse_street('flop') self._parse_street('turn') self._parse_street('river') self._parse_showdown() self._parse_pot() self._parse_board() self._parse_winners() self._parse_extra() self.parsed = True So the concrete parser need to define these methods in order in any way they want. Easy to follow, but takes longer to implement each individual concrete parser. So what about declarative? In this case Base classes (like SplittableFormat and XMLFormat) would do the heavy lifting based on regex and line/node number declarations in the concrete class, and concrete classes have no code at all, just line numbers and regexes, maybe other kind of rules. Like this: class SplittableFormat: def parse_table(): "Parses TABLE_REGEX and get information" # set attributes here def parse_players(): "parses PLAYER_REGEX and get information" # set attributes here class SpecificFormat1(SplittableFormat): TABLE_REGEX = re.compile('^(?P<table_name>.*) other info \d* etc') TABLE_LINE = 1 PLAYER_REGEX = re.compile('^Player \d: (?P<player_name>.*) has (.*) in chips.') PLAYER_LINE = 16 class SpecificFormat2(SplittableFormat): TABLE_REGEX = re.compile(r'^Tournament #(\d*) (?P<table_name>.*) other info2 \d* etc') TABLE_LINE = 2 PLAYER_REGEX = re.compile(r'^Seat \d: (?P<player_name>.*) has a stack of (\d*)') PLAYER_LINE = 14 So if I want to make it possible for non-developers to write these classes the way to go seems to be the declarative way, however, I'm almost certain I can't eliminate the declarations of regexes, which clearly needs (senior :D) programmers, so should I care about this at all? Do you think it matters to choose one over another or doesn't matter at all? Maybe if somebody wants to work on this project, they will, if not, no matter which idiom I choose. Can I "convert" non-programmers to help developing these? What are your observations? Other considerations: Imperative will allow any kind of work; there is a simple flow, which they can follow but inside that, they can do whatever they want. It would be harder to force a common interface with imperative because of this arbitrary implementations. Declarative will be much more rigid, which is a bad thing, because formats might change over time without any notice. Declarative will be harder for me to develop and takes longer time. Imperative is already ready to release. I hope a nice discussion will happen in this thread about programming idioms regarding which to use when, which is better for open source projects with different scenarios, which is better for wide range of developer skills. TL; DR: Parsing different file formats (plain text, XML) They contains same kind of information Target audience: non-developers, beginners Regex probably cannot be avoided 30-40 concrete parser classes needed Facilitate coding these concrete classes Which idiom is better?

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• Does programming knowledge have a half-life?

  - by Gary Rowe

  In answering this question, I asserted that programming knowledge has a half-life of about 18 months. In physics, we have radioactive decay which is the process by which a radioactive element transforms into something less energetic. The half-life is the measure of how long it takes for this process to result in only half of the material to remain. A parallel concept might be that over time our programming knowledge ceases to be the current idiom and eventually becomes irrelevant. Noting that a half-life is asymptotic (so some knowledge will always be relevant), what are your thoughts on this? Is 18 months a good estimate? Is it even the case? Does it apply to design patterns, but over a longer period? What are the inherent advantages/disadvantages of this half-life? Update Just found this question which covers the material fairly well: "Half of everything you know will be obsolete in 18-24 months" = ( True, or False? )

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• Why are we as an industry not more technically critical of our peers? [closed]

  - by Jarrod Roberson

  For example: I still see people in 2011 writing blog posts and tutorials that promote setting the Java CLASSPATH at the OS environment level. I see people writing C and C++ tutorials dated 2009 and newer and the first lines of code are void main(). These are examples, I am not looking for specific answers to the above questions, but to why the culture of accepting sub-par knowledge in the industry is so rampant. I see people posting these same type of empirically wrong suggestions as answers on www.stackoverflow.com and they get lots of up votes and practically no down votes! The ones that get lots of down votes are usually from answering a question that wasn't asked because of lack of reading for comprehension skills, and not incorrect answers per se. Is our industry that ignorant as a whole, I can understand the internet in general being lazy, apathetic and un-informed but our industry should be more on top of things like this and way more critical of people that are promoting bad habits and out-dated techniques and information. If we are really an engineering discipline, why aren't people held to a higher standard as they are in other engineering disciplines? I want to know why people accept bad advice, poor practices as the norm and are not more critical of their peers in the software industry.?

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• C++ Iterator lifetime and detecting invalidation

  - by DK.

  Based on what's considered idiomatic in C++11: should an iterator into a custom container survive the container itself being destroyed? should it be possible to detect when an iterator becomes invalidated? are the above conditional on "debug builds" in practice? Details: I've recently been brushing up on my C++ and learning my way around C++11. As part of that, I've been writing an idiomatic wrapper around the uriparser library. Part of this is wrapping the linked list representation of parsed path components. I'm looking for advice on what's idiomatic for containers. One thing that worries me, coming most recently from garbage-collected languages, is ensuring that random objects don't just go disappearing on users if they make a mistake regarding lifetimes. To account for this, both the PathList container and its iterators keep a shared_ptr to the actual internal state object. This ensures that as long as anything pointing into that data exists, so does the data. However, looking at the STL (and lots of searching), it doesn't look like C++ containers guarantee this. I have this horrible suspicion that the expectation is to just let containers be destroyed, invalidating any iterators along with it. std::vector certainly seems to let iterators get invalidated and still (incorrectly) function. What I want to know is: what is expected from "good"/idiomatic C++11 code? Given the shiny new smart pointers, it seems kind of strange that STL allows you to easily blow your legs off by accidentally leaking an iterator. Is using shared_ptr to the backing data an unnecessary inefficiency, a good idea for debugging or something expected that STL just doesn't do? (I'm hoping that grounding this to "idiomatic C++11" avoids charges of subjectivity...)

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• Object oriented wrapper around a dll

  - by Tom Davies

  So, I'm writing a C# managed wrapper around a native dll. The dll contains several hundred functions. In most cases, the first argument to each function is an opaque handle to a type internal to the dll. So, an obvious starting point for defining some classes in the wrapper would be to define classes corresponding to each of these opaque types, with each instance holding and managing the opaque handle (passed to its constructor) Things are a little awkward when dealing with callbacks from the dll. Naturally, the callback handlers in my wrapper have to be static, but the callbacks arguments invariable contain an opaque handle. In order to get from the static callback back to an object instance, I've created a static dictionary in each class, associating handles with class instances. In the constructor of each class, an entry is put into the dictionary, and this entry is then removed in the Destructors. When I receive a callback, I can then consult the dictionary to retrieve the class instance corresponding to the opaque reference. Are there any obvious flaws to this? Something that seems to be a problem is that the existence static dictionary means that the garbage collector will not act on my class instances that are otherwise unreachable. As they are never garbage collected, they never get removed from the dictionary, so the dictionary grows. It seems I might have to manually dispose of my objects, which is something absolutely would like to avoid. Can anyone suggest a good design that allows me to avoid having to do this?

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• What problems can arise from emulating concepts from another languages?

  - by Vandell

  I've read many times on the web that if your language doesn't support some concept, for example, object orientation, or maybe function calls, and it's considered a good practice in this other context, you should do it. The only problem I can see now is that other programmers may find your code too different than the usual, making it hard for them to program. What other problems do you think may arise from this?

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• clone() only partially doable; how to react?

  - by hllnll

  Suppose we have a class-hierarchy whose base class B requires a clone() method to be defined in its derivations. Whilst this works perfectly for most of them there is this one derivation X that holds an optional reference to a resource/object that can only be referenced from one instance of X. Whilst the rest of X can be cloned without problems this reference would have to be set to null/nil/nullptr. What is the correct way to handle this situation? X::clone() could throw an UncloneableException. Though this would be correct, it is not satisfying. Set the reference to null/nil/nullptr and leave no notice of it. The user of X has to know about Xs "particularities". Require derivations of B to define B::nearestClone(): the user of B has to be aware that the return value might not be a 1:1 clone. Something else?

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• How to mimic built-in .NET serialization idioms?

  - by Matt Enright

  I have a library (written in C#) for which I need to read/write representations of my objects to disk (or to any Stream) in a particular binary format (to ensure compatibility with C/Java library implementations). The format requires a fair amount of bit-packing and some DEFLATE'd bytestreams. I would like my library, however, to be as idiomatic .NET as possible, however, and so would like to provide an API as close as possible to the normal binary serialization process. I'm aware of the ability to implement the IFormatter interface, but being that I really am unable to reuse any part of the built-in serialization stack, is it worth doing this, or will it just bring unnecessary overhead. In other words: Implement IFormatter and co. OR Just provide "Serialize"/"Deserialize" methods that act on a Stream? A good point brought up below about needing the serialization semantics for any case involving Remoting. In a case where using MarshalByRef objects is feasible, I'm pretty sure that this won't be an issue, so leaving that aside are there any benefits or drawbacks to using the ISerializable/IFormatter versus a custom stack (or, is my understanding remoting incorrectly)?

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• Idioms for a three-state toggle?

  - by Alex Mcp

  I have a table column where each row has one of three states, and the purpose of the row is to offer manipulation AND display of this property with three states. My current development view is to have three tightly packed radio buttons with labels at the head of the columns (and every 50 rows or so) and onClick they send an AJAX request and thar she blows. This is fugly. Is there a standard idiom for a control like this? I'm currently mocking up something similar to the iPhone on/off toggle, but with a "middle" state. Any input would be welcome.

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• What features of Scala cannot be translated to Java?

  - by Paul

  The Scala compiler compiles direct to Java byte code (or .NET CIL). Some of the features of Scala could be re-done in Java straightforwardly (e.g. simple for comprehensions, classes, translating anonymous/inner functionc etc). What are the features that cannot be translated that way? That is presumably mostly of academic interest. More usefully, perhaps, what are the key features or idioms of Scala that YOU use that cannot be easily represented in Java? Are there any the other way about? Things that can be done straightforwardly in Java that have no straightforward equivalent in Scala? Idioms in Java that don't translate?

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• Famous eponymous programming techniques

  - by Alicia

  In some sports certain techniques or elements are named after the athlete who invented or first performed them—for example, Biellmann spin. Is their widespread use of such names for programming techniques and idioms? What are they? To be clear, I am explicitly not asking about algorithms, which are quite often named after their creators. For example, one is Schwartzian transform, but I can't recall any more.

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• avoiding the tedium of optional parameters

  - by Kyle

  If I have a constructor with say 2 required parameters and 4 optional parameters, how can I avoid writing 16 constructors or even the 10 or so constructors I'd have to write if I used default parameters (which I don't like because it's poor self-documentation)? Are there any idioms or methods using templates I can use to make it less tedious? (And easier to maintain?)

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• Python: if key in dict vs. try/except

  - by LeeMobile

  I have a question about idioms and readability, and there seems to be a clash of Python philosophies for this particular case: I want to build dictionary A from dictionary B. If a specific key does not exist in B, then do nothing and continue on. Which way is better? try: A["blah"] = B["blah"] except KeyError: pass or if "blah" in B: A["blah"] = B["blah"] "Do and ask for forgiveness" vs. "simplicity and explicitness". Which is better and why?

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• Idiom vs. pattern

  - by Roger Pate

  In the context of programming, how do idioms differ from patterns? I use the terms interchangeably and normally follow the most popular way I've heard something called, or the way it was called most recently in the current conversation, e.g. "the copy-swap idiom" and "singleton pattern". The best difference I can come up with is code which is meant to be copied almost literally is more often called pattern while code meant to be taken less literally is more often called idiom, but such isn't even always true. This doesn't seem to be more than a stylistic or buzzword difference. Does that match your perception of how the terms are used? Is there a semantic difference?

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• Updating a C# 2.0 events example to be idiomatic with C# 3.5?

  - by Damien Wildfire

  I have a short events example from .NET 2.0 that I've been using as a reference point for a while. We're now upgrading to 3.5, though, and I'm not clear on the most idiomatic way to do things. How would this simple events example get updated to reflect idioms that are now available in .NET 3.5? // Args class. public class TickArgs : EventArgs { private DateTime TimeNow; public DateTime Time { set { TimeNow = value; } get { return this.TimeNow; } } } // Producer class that generates events. public class Metronome { public event TickHandler Tick; public delegate void TickHandler(Metronome m, TickArgs e); public void Start() { while (true) { System.Threading.Thread.Sleep(3000); if (Tick != null) { TickArgs t = new TickArgs(); t.Time = DateTime.Now; Tick(this, t); } } } } // Consumer class that listens for events. public class Listener { public void Subscribe(Metronome m) { m.Tick += new Metronome.TickHandler(HeardIt); } private void HeardIt(Metronome m, TickArgs e) { System.Console.WriteLine("HEARD IT AT {0}",e.Time); } } // Example. public class Test { static void Main() { Metronome m = new Metronome(); Listener l = new Listener(); l.Subscribe(m); m.Start(); } }

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• Common idiom in Java to Scala, traverse/Iterate Java list into Scala list

  - by Berlin Brown

  I am processing a XML document and iterating through nodes. I want to iterate through the nodes and build a new List of some type. How would I do this with Scala: Here is my XML traverse code: def findClassRef(xmlNode: Elem) = { xmlNode\"classDef" foreach { (entry) => val name = entry \ "@name" val classid = entry \ "@classId" println(name + "//" + classid) } } Where the line of println is, I want to append elements to a list.

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• Python "Every Other Element" Idiom

  - by Matt Luongo

  Hey guys, I feel like I spend a lot of time writing code in Python, but not enough time creating Pythonic code. Recently I ran into a funny little problem that I thought might have an easy, idiomatic solution. Paraphrasing the original, I needed to collect every sequential pair in a list. For example, given the list [1,2,3,4,5,6], I wanted to compute [(1,2),(3,4),(5,6)]. I came up with a quick solution at the time that looked like translated Java. Revisiting the question, the best I could do was l = [1,2,3,4,5,6] [(l[2*x],l[2*x+1]) for x in range(len(l)/2)] which has the side effect of tossing out the last number in the case that the length isn't even. Is there a more idiomatic approach that I'm missing, or is this the best I'm going to get?

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• Rails 3: What is the proper way to respond to REST-ful actions with JSON in rails?

  - by Damien Wilson

  Hello SO. I'm trying to make an API for my rails application using JSON responses to RESTful resource controllers. This is a new experience for me, so I'm looking for some guidance and pointers. To start things off: In a rails application, what is the "proper" way to respond with JSON to REST-ful controller methods? (create, update, destroy) Is there an idiomatic way to indicate success/failure through a JSON response? Additional information: I'm currently working with rails 3.0.beta2 I would like to avoid using a plugin or gem to do the grunt work, my goal is to gain a better understanding of how to make a rails 3 API. Links to places I could find more information on the topic would also be appreciated, some quick searching on google didn't do me much good.

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• Idiomatic ruby for temporary variables within a method

  - by Andrew Grimm

  Within a method, I am using i and j as temporary variables while calculating other variables. What is an idiomatic way of getting rid of i and j once they are no longer needed? Should I use blocks for this purpose? i = positions.first while nucleotide_at_position(i-1) == nucleotide_at_position(i) raise "Assumption violated" if i == 1 i -= 1 end first_nucleotide_position = i j = positions.last while nucleotide_at_position(j+1) == nucleotide_at_position(j) raise "Assumption violated" if j == sequence.length j += 1 end last_nucleotide_position = j Background: I'd like to get rid of i and j once they are no longer needed so that they aren't used by any other code in the method. Gives my code less opportunity to be wrong. I don't know the name of the concept - is it "encapsulation"? The closest concepts I can think of are (warning: links to TV Tropes - do not visit while working) Chekhov'sGun or YouHaveOutlivedYourUsefulness. Another alternative would be to put the code into their own methods, but that may detract from readability.

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• Most idiomatic way to print a time difference in Java?

  - by Zombies

  I'm familiar with printing time difference in milliseconds: long time = System.currentTimeMillis(); //do something that takes some time... long completedIn = System.currentTimeMillis() - time(); But, is there a nice way print a complete time in a specified format (eg: HH:MM:SS) either using Apache Commons or even the dreaded platform API's Date/Time objects? In other words, what is the shortest, simplest, no nonsense way to write this in Java?

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