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  • How do you determine how coarse or fine-grained a 'responsibility' should be when using the single r

    - by Mark Rogers
    In the SRP, a 'responsibility' is usually described as 'a reason to change', so that each class (or object?) should have only one reason someone should have to go in there and change it. But if you take this to the extreme fine-grain you could say that an object adding two numbers together is a responsibility and a possible reason to change. Therefore the object should contain no other logic, because it would produce another reason for change. I'm curious if there is anyone out there that has any strategies for 'scoping', the single-responsibility principle that's slightly less objective?

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  • Right design to validate attributes of a class instance

    - by systempuntoout
    Having a simple Python class like this: class Spam(object): __init__(self, description, value): self.description = description self.value = value Which is the correct approach to check these constraints: "description cannot be empty" "value must be greater than zero" Should i: 1.validate data before creating spam object ? 2.check data on __init__ method ? 3.create an is_valid method on Spam class and call it with spam.isValid() ? 4.create an is_valid static method on Spam class and call it with Spam.isValid(description, value) ? 5.check data on setters? 6.... Could you recommend a well designed\Pythonic\not verbose (on class with many attributes)\elegant approach?

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  • Documentation style: how do you differentiate variable names from the rest of the text within a comm

    - by Alix
    Hi, This is a quite superfluous and uninteresting question, I'm afraid, but I always wonder about this. When you're commenting code with inline comments (as opposed to comments that will appear in the generated documentation) and the name of a variable appears in the comment, how do you differentiate it from normal text? E.g.: // Try to parse type. parsedType = tryParse(type); In the comment, "type" is the name of the variable. Do you mark it in any way to signify that it's a symbol and not just part of the comment's text? I've seen things like this: // Try to parse "type". // Try to parse 'type'. // Try to parse *type*. // Try to parse <type>. // Try to parse [type]. And also: // Try to parse variable type. (I don't think the last one is very helpful; it's a bit confusing; you could think "variable" is an adjective there) Do you have any preference? I find that I need to use some kind of marker; otherwise the comments are sometimes ambiguous, or at least force you to reread them when you realise a particular word in the comment was actually the name of a variable. (In comments that will appear in the documentation I use the appropriate tags for the generator, of course: @code, <code></code>, etc) Thanks!

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  • Reference table values in a war against magic numbers

    - by Alex N.
    This question bugged me for years now and can't seem to find good solution still. I working in PHP and Java but it sounds like this maybe language-agnostic :) Say we have a standard status reference table that holds status ids for some kind of entity. Further let's assume the table will have just 5 values, and will remain like this for a long time, maybe edited occasionally with addition of a new status. When you fetch a row and need to see what status it is you have 2 options(as I see it at least) - put it straight ID values(magic numbers that is) or use a named constant. Latter seem much cleaner, the question though is where those named constants should leave? In a model class? In a class that uses this particular constant? Somewhere else?

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  • Tool that auto-generate a code for accesing a xml-file

    - by alex
    My application have a configuration xml-file. That file contains more than 50 program settings. At the present time I read and save each program setting separately. I guess It is not effi?iently for such tasks. I need something that can auto-generate a code for load and save my program settings using predefined xml-schema. I found a dataset in Add New Item dialog. Unfortunately, i cannot add new code to dataset1 such as events in set-accessors of properties because of this // Changes to this file may cause incorrect behavior and will be lost if // the code is regenerated. Maybe, there is a tool that allows a user to generate a wrapper for accesing a xml-file ? Such as DataSet1, but with availability to add events.

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  • When to rewrite vs. upgrade?

    - by MrGumbe
    All custom legacy software needs changing, or so say our users. Sometimes they want a feature or two added and all that is necessary to change a bit of code, add a control, or some other minor upgrade task. Sometimes they want to ditch their error-prone VB5 desktop solution and rewrite the whole thing as a rich Web 2.0 ASP.NET MVC application. More often, however, the scope of changes to legacy functionality lies somewhere between these two extremes. What rules of thumb to you use to decide whether you should upgrade an existing application or start from scratch?

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  • Dependency injection in C++

    - by Yorgos Pagles
    This is also a question that I asked in a comment in one of Miško Hevery's google talks that was dealing with dependency injection but it got buried in the comments. I wonder how can the factory / builder step of wiring the dependencies together can work in C++. I.e. we have a class A that depends on B. The builder will allocate B in the heap, pass a pointer to B in A's constructor while also allocating in the heap and return a pointer to A. Who cleans up afterwards? Is it good to let the builder clean up after it's done? It seems to be the correct method since in the talk it says that the builder should setup objects that are expected to have the same lifetime or at least the dependencies have longer lifetime (I also have a question on that). What I mean in code: class builder { public: builder() : m_ClassA(NULL),m_ClassB(NULL) { } ~builder() { if (m_ClassB) { delete m_ClassB; } if (m_ClassA) { delete m_ClassA; } } ClassA *build() { m_ClassB = new class B; m_ClassA = new class A(m_ClassB); return m_ClassA; } }; Now if there is a dependency that is expected to last longer than the lifetime of the object we are injecting it into (say ClassC is that dependency) I understand that we should change the build method to something like: ClassA *builder::build(ClassC *classC) { m_ClassB = new class B; m_ClassA = new class A(m_ClassB, classC); return m_ClassA; } What is your preferred approach?

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  • How to use interfaces in exception handling

    - by vikp
    Hi, I'm working on the exception handling layer for my application. I have read few articles on interfaces and generics. I have used inheritance before quite a lot and I'm comfortable with in that area. I have a very brief design that I'm going to implement: public interface IMyExceptionLogger { public void LogException(); // Helper methods for writing into files,db, xml } I'm slightly confused what I should be doing next. public class FooClass: IMyExceptionLogger { // Fields // Constructors } Should I implement LogException() method within FooClass? If yes, than I'm struggling to see how I'm better of using an interface instead of the concrete class... I have a variety of classes that will make a use of that interface, but I don't want to write an implementation of that interface within each class. In the same time If I implement an interface in one class, and then use that class in different layers of the application I will be still using concrete classes instead of interfaces, which is a bad OO design... I hope this makes sense. Any feedback and suggestions are welcome. Please notice that I'm not interested in using net4log or its competitors because I'm doing this to learn. Thank you Edit: Wrote some more code. So I will implement variety of loggers with this interface, i.e. DBExceptionLogger, CSVExceptionLogger, XMLExceptionLogger etc. Than I will still end up with concrete classes that I will have to use in different layers of my application.

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  • Are ASCII diagrams worth my time?

    - by Jesse Stimpson
    Are ASCII diagrams within source code worth the time they take to create? I could create a bitmap diagram much faster, but images are much more difficult to in line in a source file (until VS2010). For the record, I'm not talking about decorative ASCII art. Here's an example of a diagram I recently created for my code that I probably could have constructed in half the time in MS Paint. Scenario A: v (U)_________________(N)_______<--(P) Legend: ' / | J = ... ' / | P = ... ' /d | U = ... ' / | v = ... ' / | d = ... '/ | N = ... (J) | | | |___________________|

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  • help me to choose between two designs

    - by alex
    // stupid title, but I could not think anything smarter I have a code (see below, sorry for long code but it's very-very simple): namespace Option1 { class AuxClass1 { string _field1; public string Field1 { get { return _field1; } set { _field1 = value; } } // another fields. maybe many fields maybe several properties public void Method1() { // some action } public void Method2() { // some action 2 } } class MainClass { AuxClass1 _auxClass; public AuxClass1 AuxClass { get { return _auxClass; } set { _auxClass = value; } } public MainClass() { _auxClass = new AuxClass1(); } } } namespace Option2 { class AuxClass1 { string _field1; public string Field1 { get { return _field1; } set { _field1 = value; } } // another fields. maybe many fields maybe several properties public void Method1() { // some action } public void Method2() { // some action 2 } } class MainClass { AuxClass1 _auxClass; public string Field1 { get { return _auxClass.Field1; } set { _auxClass.Field1 = value; } } public void Method1() { _auxClass.Method1(); } public void Method2() { _auxClass.Method2(); } public MainClass() { _auxClass = new AuxClass1(); } } } class Program { static void Main(string[] args) { // Option1 Option1.MainClass mainClass1 = new Option1.MainClass(); mainClass1.AuxClass.Field1 = "string1"; mainClass1.AuxClass.Method1(); mainClass1.AuxClass.Method2(); // Option2 Option2.MainClass mainClass2 = new Option2.MainClass(); mainClass2.Field1 = "string2"; mainClass2.Method1(); mainClass2.Method2(); Console.ReadKey(); } } What option (option1 or option2) do you prefer ? In which cases should I use option1 or option2 ? Is there any special name for option1 or option2 (composition, aggregation) ?

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  • How to provide global functionality in multi-user database app

    - by Mike B
    I have been building a multi-user database application (in C#/WPF 4.0) that manages tasks for all employees of a company. I now need to add some functionality such as sending an email reminder to someone when a critical task is due. How should this be done? Obviously I don’t want every instance of the program to be performing this function (Heh each user would get 10+ emails). Should I add the capability to the application as a "Mode" and then run a copy on the database server in this mode or would it be better to create a new app altogether to perform "Global" type tasks? Is there a better way?

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  • Is it a good idea to define a variable in a local block for a case of a switch statement?

    - by Paperflyer
    I have a rather long switch-case statement. Some of the cases are really short and trivial. A few are longer and need some variables that are never used anywhere else, like this: switch (action) { case kSimpleAction: // Do something simple break; case kComplexAction: { int specialVariable = 5; // Do something complex with specialVariable } break; } The alternative would be to declare that variable before going into the switch like this: int specialVariable = 5; switch (action) { case kSimpleAction: // Do something simple break; case kComplexAction: // Do something complex with specialVariable break; } This can get rather confusing since it is not clear to which case the variable belongs and it uses some unnecessary memory. However, I have never seen this usage anywhere else. Do you think it is a good idea to declare variables locally in a block for a single case?

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  • Rapid Opening and Closing System.IO.StreamWriter in C#

    - by ccomet
    Suppose you have a file that you are programmatically logging information into with regards to a process. Kinda like your typical debug Console.WriteLine, but due to the nature of the code you're testing, you don't have a console to write onto so you have to write it somewhere like a file. My current program uses System.IO.StreamWriter for this task. My question is about the approach to using the StreamWriter. Is it better to open just one StreamWriter instance, do all of the writes, and close it when the entire process is done? Or is it a better idea to open a new StreamWriter instance to write a line into the file, then immediately close it, and do this for every time something needs to be written in? In the latter approach, this would probably be facilitated by a method that would do just that for a given message, rather than bloating the main process code with excessive amounts of lines. But having a method to aid in that implementation doesn't necessarily make it the better choice. Are there significant advantages to picking one approach or the other? Or are they functionally equivalent, leaving the choice on the shoulders of the programmer?

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  • Where to put a piece of code in Ruby on Rails?

    - by yuval
    I have a post controller that has many comments. The post model has a field called has_comments which is a boolean (so I can quickly select from the database only posts that have comments). To create a new comment for a post, I use the create action of my comments controller. After I create the comment I need to update my post's has_comments field and set it to true. I can update this field from the create action of my comments controller, but that doesn't seem right - I feel that I should really be using the post's update action, but I'm not sure if it's right to call it (via send?) from the create action of the comments controller. Where should the code for updating the post be? Thank you!

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  • what if i keep my class members are public?

    - by anish
    In c++ instance variables are private by default,in Python variables are public by default i have two questions regarding the same:- 1: why Python have all the members are public by default? 2: People say you should your member data should be private what if i make my data to be public? what are the disadvantages of this approch? why it is a bad design?

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  • Python-based password tracker (or dictionary)

    - by Arrieta
    Hello: Where we work we need to remember about 10 long passwords which need to change every so often. I would like to create a utility which can potentially save these passwords in an encrypted file so that we can keep track of them. I can think of some sort of dictionary passwd = {'host1':'pass1', 'host2':'pass2'}, etc, but I don't know what to do about encryption (absolutely zero experience in the topic). So, my question is really two questions: Is there a Linux-based utility which lets you do that? If you were to program it in Python, how would you go about it? A perk of approach two, would be for the software to update the ssh public keys after the password has been changed (you know the pain of updating ~15 tokens once you change your password). As it can be expected, I have zero control over the actual network configuration and the management of scp keys. I can only hope to provide a simple utility to me an my very few coworkers so that, if we need to, we can retrieve a password on demand. Cheers.

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  • SELECT product from subclass: How many queries do I need?

    - by Stefano
    I am building a database similar to the one described here where I have products of different type, each type with its own attributes. I report a short version for convenience product_type ============ product_type_id INT product_type_name VARCHAR product ======= product_id INT product_name VARCHAR product_type_id INT -> Foreign key to product_type.product_type_id ... (common attributes to all product) magazine ======== magazine_id INT title VARCHAR product_id INT -> Foreign key to product.product_id ... (magazine-specific attributes) web_site ======== web_site_id INT name VARCHAR product_id INT -> Foreign key to product.product_id ... (web-site specific attributes) This way I do not need to make a huge table with a column for each attribute of different product types (most of which will then be NULL) How do I SELECT a product by product.product_id and see all its attributes? Do I have to make a query first to know what type of product I am dealing with and then, through some logic, make another query to JOIN the right tables? Or is there a way to join everything together? (if, when I retrieve the information about a product_id there are a lot of NULL, it would be fine at this point). Thank you

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  • Should every class have its own namespace?

    - by thehouse
    Something that has been troubling me for a while: The current wisdom is that types should be kept in a namespace that only contains functions which are part of the type's non-member interface (see C++ Coding Standards Sutter and Alexandrescu or here) to prevent ADL pulling in unrelated definitions. Does this imply that all classes must have a namespace of their own? If we assume that a class may be augmented in the future by the addition of non-member functions, then it can never be safe to put two types in the same namespace as either one of them may introduce non-member functions that could interfere with the other. The reason I ask is that namespaces are becoming cumbersome for me. I'm writing a header-only library and I find myself using classes names such as project::component::class_name::class_name. Their implementations call helper functions but as these can't be in the same namespace they also have to be fully qualified!

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  • Which options do I have for Java process communication?

    - by Dmitriy Matveev
    We have a place in a code of such form: void processParam(Object param) { wrapperForComplexNativeObject result = jniCallWhichMayCrash(param); processResult(result); } processParam - method which is called with many different arguments. jniCallWhichMayCrash - a native method which is intended to do some complex processing of it's parameter and to create some complex object. It can crash in some cases. wrapperForComplexNativeObject - wrapper type generated by SWIG processResult - a method written in pure Java which processes it's parameter by creation of several kinds (by the kinds I'm not meaning classes, maybe some like hierarchies) of objects: 1 - Some non-unique objects which are referencing each other (from the same hierarchy), these objects can have duplicates created from the invocations of processParam() method with different parameter values. Since it's costly to keep all the duplicates it's necessary to cache them. 2 - Some unique objects which are referencing each other (from the same hierarchy) and some of the objects of 1st kind. After processParam is executed for each of the arguments from some set the data created in processResult will be processed together. The problem is in fact that jniCallWhichMayCrash method may crash the entire JVM and this will be very bad. The reason of crash may be such that it can happen for one argument value and not for the other. We've decided that it's better to ignore crashes inside of JVM and just skip some chunks of data when such crashes occur. In order to do this we should run processParam function inside of separate process and pass the result somehow (HOW? HOW?! This is a question) to the main process and in case of any crashes we will only lose some part of data (It's ok) without lose of everything else. So for now the main problem is implementation of transport between different processes. Which options do I have? I can think about serialization and transmitting of binary data by the streams, but serialization may be not very fast due to object complexity. Maybe I have some other options of implementing this?

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