Primitive constructors vs casting for conversion
- by peter
What is the difference between:
long myLong;
float myFloat = (float) myLong;
and:
float myFloat = float(myLong);
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Anonymous users support vs Google bot
- by Andy
I have a User class in my web app that represents a user currently logged in. Every time a user vists a page, a User instance is populated based on authentication data supplied in cookies. A User instance is created even if an anonymous user logs in - and a corresponding new record is created in the User table in the database. This approach allows me to save some state info for the current user regardless of its type. The problem however with this approach is the Google bot, and other non-human web organisms crawling my pages. Every time a bot starts to walk around the site, thousands of useless records will be created in the database, each of them only to be used for a single page. Question: what is the best trade off? How to support anonymous users, save their state, and don't get too much overhead because of cookieless bots?Read the article
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Factory vs instance constructors
- by Neil N
I can't think of any reasons why one is better than the other. Compare these two implementations: public class MyClass { public myClass(string fileName) { // some code... } } as opposed to: public class MyClass { private myClass(){} public static Create(string fileName) { // some code... } } There are some places in the .Net framework that use the static method to create instances. At first I was thinking, it registers it's instances to keep track of them, but regular constructors could do the same thing through the use of private static variables. What is the reasoning behind this style?Read the article
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Table Naming Dilemma: Singular vs. Plural Names
- by ProfK
Convention has it that table names should be the singular of the entity that they store attributes of. I dislike any T-SQL that requires square brackets around names, but I have renamed a Users table to the singular, forever sentencing those using the table to sometimes have to use brackets. My gut feel is that it is more correct to stay with the singular, but my gut feel is also that brackets indicate undesirables like column names with spaces in them etc. Should I stay, or should I go?Read the article
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Debug vs Trace in C#
- by koumides
All, As I understand statements like Debug.WriteLine() will not stay in the code in the Release build. On the other hand Trace.WriteLine() will stay in the code in the Release build. What is controling this behaviour? Does the C# compiler ignores everything from the System.Diagnostics.Debug class when the DEBUG is defined? I am just trying to understand the internals of C# and just curious. Thanks, MKRead the article
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Ruby proc vs lambda in initialize()
- by Jimmy Chu
I found out this morning that proc.new works in a class initialize method, but not lambda. Concretely, I mean: class TestClass attr_reader :proc, :lambda def initialize @proc = Proc.new {puts "Hello from Proc"} @lambda = lambda {puts "Hello from lambda"} end end c = TestClass.new c.proc.call c.lambda.call In the above case, the result will be: Hello from Proc test.rb:14:in `<main>': undefined method `call' for nil:NilClass (NoMethodError) Why is that? Thanks!Read the article
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Category VS logger tags in jboss-log4j.xml
- by Vladimir Bezugliy
What should we use in jboss-log4j.xml in order to turn on/off traces for our product - "category" or "logger" tag? By default JBoss uses "category" in jboss-log4j.xml. But as far as I know "category" is deprecated and "logger" should be used instead. Why JBoss uses deprecated "category" tag in a new product?Read the article
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Sesion timout vs Form Authentication timeout
- by Costa
Hi What is the difference between a abandon Session and a cookie timeout, what if the session is abandon and the cookie is still alive, is that can lead to a problem? <sessionState timeout="1" /> <authentication mode="Forms"> <forms loginUrl="login.aspx" timeout="1" /> </authentication> ThanksRead the article
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Domain object validation vs view model validation
- by Brendan Vogt
I am using ASP.NET MVC 3 and I am using FluentValidation to validate my view models. I am just a little concerned that I might not be on the correct track. As far as what I know, model validation should be done on the domain object. Now with MVC you might have multiple view models that are similar that needs validation. What happens if a property from a domain object occurs in more than one view model? Now you are validating the same property twice, and they might not even be in sync. So if I have a User domain object then I would like to do validation on this object. Now what happens if I have UserAViewModel and UserBViewModel, so now it is multiple validations that needs to be done. The scenario above is just an example, so please don't critise on it.Read the article
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Sbyte[] vs byte[][] using methods
- by blgnklc
It is written byte[][] getImagesForFields(java.lang.String[] fieldnames) Gets an array of images for the given fields. On the other hand, as long as I use the method in the web application project built on asp.net 2.o using c#; the provided web method declared above, returns sbyte; Have a look my code below; formClearanceService.openSession(imageServiceUser); formClearanceService.prepareInstance(formId); byte[][] fieldImagesList = formClearanceService.getImagesForFields(fieldNames); formClearanceService.closeSession(); thus I get the following error: Cannot implicitly convert type 'sbyte[]' to 'byte[][]' So now, 1- should I ask the web service provider what is going on? or 2- any other way that can use the sbyte as I was suppose to use byte[][] like following using: byte[] ssss = fieldImagesList [0]..Read the article
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C++ STL Map vs Vector speed
- by sub
In the interpreter for my experimental programming language I have a symbol table. Each symbol consists of a name and a value (the value can be e.g.: of type string, int, function, etc.). At first I represented the table with a vector and iterated through the symbols checking if the given symbol name fitted. Then I though using a map, in my case map<string,symbol>, would be better than iterating through the vector all the time but: It's a bit hard to explain this part but I'll try. If a variable is retrieved the first time in a program in my language, of course its position in the symbol table has to be found (using vector now). If I would iterate through the vector every time the line gets executed (think of a loop), it would be terribly slow (as it currently is, nearly as slow as microsoft's batch). So I could use a map to retrieve the variable: SymbolTable[ myVar.Name ] But think of the following: If the variable, still using vector, is found the first time, I can store its exact integer position in the vector with it. That means: The next time it is needed, my interpreter knows that it has been "cached" and doesn't search the symbol table for it but does something like SymbolTable.at( myVar.CachedPosition ). Now my (rather hard?) question: Should I use a vector for the symbol table together with caching the position of the variable in the vector? Should I rather use a map? Why? How fast is the [] operator? Should I use something completely different?Read the article
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Lisp vs Python -- Static Compilation
- by yodie
Why can Lisp with all its dynamic features be statically compiled but Python cannot (without losing all its dynamic features)?Read the article
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Java BufferedReader behavior in CSV vs TXT file
- by Gabriel
If i try to read a CSV file called csv_file.csv. The problem is that when i read lines with BufferedReader.readLine() it skips the first line with months. But when i rename the file to csv_file.txt it reads it allright and it's not skipping the first line. Is there an undocumented "feature" of BufferedReader that i'm not aware? Example of file: Months, SEP2010, OCT2010, NOV2010 col1, col2, col3, col4, col5 aaa,,sdf,"12,456",bla bla bla, xsaffadfafda and so on, and so on, "10,00", xxx, xxx The code: FileInputStream stream = new FileInputStream(UploadSupport.TEMPORARY_FILES_PATH+fileName); BufferedReader br = new BufferedReader(new InputStreamReader(stream, "UTF-8")); String line = br.readLine(); String months[] = line.split(","); while ((line=br.readLine())!=null) { /*parse other lines*/ }Read the article
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ModelName(django.contrib.auth.models.User) vs ModelName(models.Model)
- by amr.negm
I am developing a django project. I created some apps, some of those are related to User model, for instance, I have a feeds app that handles user feeds, and another app that deals with extra user data like age, contacts, and friends. for each of these, I created a table that should be connected to the User model, which I using for storing and authenticating users. I found two ways to deal with this issue. One, is through extending User model to be like this: ModelName(User): friends = models.ManyToMany('self') ..... Two, is through adding a foreign key to the new table like this: ModelName(models.Model): user = models.ForeignKey(User, unique=True) friends = friends = models.ManyToMany('self') ...... I can't decide which to use in which case. in other words, what are the core differences between both?Read the article
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C++ Array vs vector
- by blue_river
when using C++ vector, time spent is 718 milliseconds, while when I use Array, time is almost 0 milliseconds. Why so much performance difference? int _tmain(int argc, _TCHAR* argv[]) { const int size = 10000; clock_t start, end; start = clock(); vector<int> v(size*size); for(int i = 0; i < size; i++) { for(int j = 0; j < size; j++) { v[i*size+j] = 1; } } end = clock(); cout<< (end - start) <<" milliseconds."<<endl; // 718 milliseconds int f = 0; start = clock(); int arr[size*size]; for(int i = 0; i < size; i++) { for(int j = 0; j < size; j++) { arr[i*size+j] = 1; } } end = clock(); cout<< ( end - start) <<" milliseconds."<<endl; // 0 milliseconds return 0; }Read the article
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Warning vs. error
- by Samuel
I had an annoying issue, getting a "Possible loss of precision" error when compiling my Java program on BlueJ (But from what i read this isn't connected to a specific IDE). I was surprised by the fact that the compiler told me there is a possible loss of precision and wouldnt let me compile/run the program. Why is this an error and not a warning saying you might loose precision here, if you don't want that change your code? The program runs just fine when i drop the float values, it wouldn't matter since there is no point (e.g [143.08, 475.015]) on my screen. On the other hand when i loop through an ArrayList and in this loop i have an if clause removing elements from the ArrayList it runs fine, just throws an error and doesn't display the ArrayList [used for drawing circles] for a fraction of a second. This appears to me as a severe error but doesn't cause (hardly) any troubles, while i wouldn't want to have such a thing in my code at all. What's the boundary?Read the article
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F# ref-mutable vars vs object fields
- by rwallace
I'm writing a parser in F#, and it needs to be as fast as possible (I'm hoping to parse a 100 MB file in less than a minute). As normal, it uses mutable variables to store the next available character and the next available token (i.e. both the lexer and the parser proper use one unit of lookahead). My current partial implementation uses local variables for these. Since closure variables can't be mutable (anyone know the reason for this?) I've declared them as ref: let rec read file includepath = let c = ref ' ' let k = ref NONE let sb = new StringBuilder() use stream = File.OpenText file let readc() = c := stream.Read() |> char // etc I assume this has some overhead (not much, I know, but I'm trying for maximum speed here), and it's a little inelegant. The most obvious alternative would be to create a parser class object and have the mutable variables be fields in it. Does anyone know which is likely to be faster? Is there any consensus on which is considered better/more idiomatic style? Is there another option I'm missing?Read the article
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Physical Cores vs Virtual Cores in Parallelism
- by Code Curiosity
When it comes to virtualization, I have been deliberating on the relationship between the physical cores and the virtual cores, especially in how it effects applications employing parallelism. For example, in a VM scenario, if there are less physical cores than there are virtual cores, if that's possible, what's the effect or limits placed on the application's parallel processing? I'm asking, because in my environment, it's not disclosed as to what the physical architecture is. Is there still much advantage to parallelizing if the application lives on a dual core VM hosted on a single core physical machine?Read the article
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iPhone SDK development obj-C vs interface builder
- by Amy
I'm new to the iOS platform. I'm not clear on the purpose of the interface builder. It looks like I can avoid using it entirely and just write all the code in objective c. am I right? is there anything that IB can do but obj-c cannot? It reminds me of visual basic 6.Read the article
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openmp vs opencl for computer vision
- by user1235711
I am creating a computer vision application that detect objects via a web camera. I am currently focusing on the performance of the application My problem is in a part of the application that generates the XML cascade file using Haartraining file. This is very slow and takes about 6days . To get around this problem I decided to use multiprocessing, to minimize the total time to generate Haartraining XML file. I found two solutions: opencl and (openMp and openMPI ) . Now I'm confused about which one to use. I read that opencl is to use multiple cpu and GPU but on the same machine. Is that so? On the other hand OpenMP is for multi-processing and using openmpi we can use multiple CPUs over the network. But OpenMP has no GPU support. Can you please suggest the pros and cons of using either of the libraries.Read the article
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Zend Framework: Controller Plugins vs Action Helpers
- by Laimoncijus
Could someone give few tips and/or examples how Controller Plugins and Action Helpers are different? Are there situations where particular task could be accomplished with one but not another? For me they both look more or less the same and I'm often having trouble having to decide when to use what... Are there any big differences?Read the article
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.Net Hashtable - Contains vs ContainsKey
- by Midhat
I just notices the HashTable objects have a Contains and CotainsKey method, with same description. So are they just synonyms or is there som edifference behind the scenesRead the article
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Cannot change the height of a combo box in the VS Dialog Editor
- by Hamish Morrison
Any combo box I create seems to be stuck at 12 dialog units in height. Microsoft's guidelines for spacing and sizing of controls in dialog boxes state that a combo box should be 14 dialog units high. I have even tried editing the resource file in notepad and recompiling in Visual Studio without opening the resource editor - but the combo boxes are still the wrong size! Any ideas?Read the article
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ASP.NET MVC image upload store location (db vs filesystem)
- by adrin
I am writing web application using ASP.NET MVC + NHibernate + Postres stack. I wonder if images uploaded should be stored in database as binary blobs or on filesystem (and reference only in db). One advantage of db storage I can think of is easy backup/recovery of all data without reverting to filesystem copy tools. On the other hand I suspect that filesystem access may be faster (but is it especially when dealing with many concurrent requests?) What are your suggestions?Read the article
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String comparison in Python: is vs. ==
- by Coquelicot
I noticed a Python script I was writing was acting squirrelly, and traced it to an infinite loop, where the loop condition was "while line is not ''". Running through it in the debugger, it turned out that line was in fact ''. When I changed it to != rather than 'is not', it worked fine. I did some searching, and found this question, the top answer to which seemed to be just what I needed. Except the answer it gave was counter to my experience. Specifically, the answerer wrote: For all built-in Python objects (like strings, lists, dicts, functions, etc.), if x is y, then x==y is also True. I double-checked the type of the variable, and it was in fact of type str (not unicode or something). Is his answer just wrong, or is there something else afoot? Also, is it generally considered better to just use '==' by default, even when comparing int or Boolean values? I've always liked to use 'is' because I find it more aesthetically pleasing and pythonic (which is how I fell into this trap...), but I wonder if it's intended to just be reserved for when you care about finding two objects with the same id.Read the article
