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  • Exclamation mark used with assert method in its parameters.

    - by Maxsy
    Okay this has been lingering in my head for quite a while now. In ruby on rails unit testing there is an exclamation mark with the assert method. Here is an example test "No empty values to be inserted" do product = Produce.new assert !product.save end Let me know the function of the exclamation mark. Quick replies appreciated. Thanks.

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  • Does Perl auto-vivify variables used as references in subroutine calls?

    - by FM
    I've declared 2010 to be the year of higher-order programming, so I'm learning Haskell. The introduction has a slick quick-sort demo, and I thought, "Hey, that's easy to do in Perl". It turned to be easier than I expected. Note that I don't have to worry about whether my partitions ($less and $more) are defined. Normally you can't use an undefined value as an array reference. use strict; use warnings; use List::MoreUtils qw(part); my @data = (5,6,7,4,2,9,10,9,5,1); my @sorted = qsort(@data); print "@sorted\n"; sub qsort { return unless @_; my $pivot = shift @_; my ($less, $more) = part { $_ < $pivot ? 0 : 1 } @_; # Works, even though $less and $more are sometimes undefined. return qsort(@$less), $pivot, qsort(@$more); } As best I can tell, Perl will auto-vivify a variable that you try to use as a reference -- but only if you are passing it to a subroutine. For example, my call to foo() works, but not the attempted print. use Data::Dumper qw(Dumper); sub foo { print "Running foo(@_)\n" } my ($x); print Dumper($x); # Fatal: Can't use an undefined value as an ARRAY reference. # print @$x, "\n"; # But this works. foo(@$x); # Auto-vivification: $x is now []. print Dumper($x); My questions: Am I understanding this behavior correctly? What is the explanation or reasoning behind why Perl does this? Is this behavior explained anywhere in the docs?

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  • What methods are used to visualize a 4-dimensional Array?

    - by Atomiton
    An Array ( a row of elements ): [ ][ ][ ][ ][ ][ ] A 2-D Array ( a table ): [ ][ ][ ][ ][ ][ ] [ ][ ][ ][ ][ ][ ] [ ][ ][ ][ ][ ][ ] [ ][ ][ ][ ][ ][ ] A 3-D Array: //Imagine the above table as a cube ( a table with depth ) How does one visualize a 4-D array? The closest I can come is multiple cubes, so for int[,,,] [5,10,2,7] would be cube 5, row 10, column 2, layer(depth) 7. I'm not sure if this is the best way to visualize a 4-D array, though... and I'm not sure it's the best way to teach it... however it does have the advantage of being extensible ( a row cubes, a table of cubes, a cube of cubes ( 6-d array ) Cubes through time is another way that I can think of it. Am I on the right track here?

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  • Help needed with MySQL query to join data spanning multiple tables with data used as column names

    - by gurun8
    I need a little help putting together a SQL query that will give me the following resultsets: and The data model looks like this: The tricky part for me is that the columns to the right of the "Product" in the resultset aren't really columns in the database but rather key/value pairs spanned across the data model. Table data is as follows: My apologies in advance for the image heavy question and the image quality. This just seemed like the easiest way to convey the information. It'll probably take someone less time to write the query statement to achieve the results than it did for me to assemble this question. By the way, the "product_option" table image is truncated but it illustrated the general idea of the data structure. The MySQL server version is 5.1.45.

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  • Rails: Accessing the username/password used for HTTP Basic Auth?

    - by Shpigford
    I'm building a basic API where user information can be retrieved after that user's login and password are correctly sent. Right now I'm using something like this: http://foo:[email protected]/api/user.xml So, what I need to do is access the user/password sent in the request (the foo and bar) but am not sure how to access that info in a Rails controller. Then I'd check those variables via a quick User.find and then set those as the username and password variables for authenticate_or_request_with_http_basic. It's possible I'm looking at this at the completely wrong way, but that's where I'm at right now. :)

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  • Can one TabBarItem be used for two different ViewControllers?

    - by Kash
    I am creating an app with three tabBarItems, but I want to control four ViewControlers with three tabBars. I am trying to use one tabBar for two different viewcontrollers. I am able to change the tabBartitle and icon upon tap, but I cannot reset it so it can go back to it's previous status with previous title and icon. Also, I am confused about using the tabBarController or just tabBar and to call what function to reload/refresh the tabBar status and where exactly? I am fairly new to the iPhone SD, please describe your answer clearly any help will be highly appreciated.

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  • How to solve the problem of not being informed of successful payments by the 3rd party system used b

    - by user68759
    I have a subscription based website that interacts with a 3rd party system to handle the payments. The steps to process a new subscriber registration are as follow: The subscriber enters his/her details in the subscription form and click on the submit button. Assuming the details specified are valid, a new record is created in the database to store these details. The subscriber is then redirected to the website of the 3rd party system (similar to paypal) to process the payment. Once the payment is succesful, the 3rd party website then redirect the subscriber back to our website. At this time, I know that the payment was succesful, so the record in the database is updated to indicate that payment has been made successfully. A problem that I have found occurring quite often is that if a subscriber pays but does not complete the process correctly (e.g. uses the back browser, closes the window), his/her record in the database doesn't get updated about this. Accordingly, I don't know if s/he has paid by just looking the record and need to wait for the report from the 3rd party system to find this out. How do you solve this problem? PS. One of the main reasons to store their details into the database before the payment process is done is so they can come back to complete the payment without re-entering their details again. For example, when their credit cards were rejected by the 3rd party system and they need to sort this out with their financial institution which may take a while.

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  • Are evolutionary algorithms and neural networks used in the same problem domains?

    - by Joe Holloway
    I am trying to get a feel for the difference between the various classes of machine-learning algorithms. I understand that the implementations of evolutionary algorithms are quite different from the implementations of neural networks. However, they both seem to be geared at determining a correlation between inputs and outputs from a potentially noisy set of training/historical data. From a qualitative perspective, are there problem domains that are better targets for neural networks as opposed to evolutionary algorithms? I've skimmed some articles that suggest using them in a complementary fashion. Is there a decent example of a use case for that? Thanks

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  • MySQL is returning an "column ambiguous" error when it used to work before I upgraded...

    - by Ronedog
    I recently upgraded MySQL to 5.1.41. Before the upgrade the following SQL worked (or at least I thought I remembered it working...it has been a few weeks since designing this...). Now the SQL gives me an error stating that the "archived" column is ambiguous. How can I write this differently, or is there a different problem I'm not aware of? I simply want to return the "unit_id", "lease_count" (stored in another table with a unit_id that should correspond with the "a.unit_id"), and "lease_archived_count (stored in another table with a unit_id that should correspond with the "a.unit_id"). SELECT a.unit_id, (SELECT count(*) FROM o_leases WHERE unit_id = a.unit_id AND archived = 0) as lease_count, (SELECT count(*) FROM o_leases WHERE unit_id = a.unit_id AND archived = 1) as lease_archive_count FROM p_unit a, properties b, portfolio c WHERE a.property_id = b.properties_id AND b.portfolio_id = c.portfolio_id AND a.archived = 0 Thanks for your help.

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  • Chrome is leaking memory, when jQuery is used on events?

    - by user269386
    Hi, I'm experiencing an increase of memory usage, when I use the jQuery-eventhandling in Chrome. I've tested it with IE and FF as well, but there I couldn't see a suspicious rise of memory-usage, compared to Chrome. I'm using Chrome version 4.0.223.16 (unfortunately I'm forced to use this version, here) Simple example here. Just scroll with the mousewheel in the red box and open the Chrome-taskmanager and you will see an increase of memory which won't be released anymore: <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <head> <script type="text/javascript" src="js/libs/jquery-1.4.2.min.js"></script> <script type="text/javascript"> jQuery(function () { jQuery("#div1").bind("mousewheel", function (event) { event.preventDefault(); }); }); </script> </head> <body> <div id="div1" style="width: 100px; height: 100px; background-color: red;"></div> </body> </html> Does anyone have experienced the same problem (or is it maybe solvend with a different version of chrome)? And does anyone have a fix for it? thanks

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  • RecursiveIterator: used to explode tree structure, or only flatten?

    - by Stephen J. Fuhry
    There are tons of examples of using the RecursiveIterator to flatten a tree structure.. but what about using it to explode a tree structure? Is there an elegant way to use this, or some other SPL library to recursively build a tree (read: turn a flat array into array of arbitrary depth) given a table like this: SELECT id, parent_id, name FROM my_tree EDIT: You know how you can do this with Directories? $it = new RecursiveDirectoryIterator("/var/www/images"); foreach(new RecursiveIteratorIterator($it) as $file) { echo $file . PHP_EOL; } .. What if you could do something like this: $it = new RecursiveParentChildIterator($result_array); foreach(new RecursiveIteratorIterator($it) as $group) { echo $group->name . PHP_EOL; echo implode(PHP_EOL, $group->getChildren()) . PHP_EOL . PHP_EOL; } :END EDIT

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  • Why JavaScript dialogs (alert/prompt/confirm) are not widely used and not under active development?

    - by serg555
    If there is a need to display some simple confirmation popup, most developers would rather install jQuery, find some dialog plugin for it, skin it, than put a one liner: if(confirm("Are you sure?")) { ... } Using alert() for displaying error messages is considered cheap. And how many sites can you name that are usingprompt()? So, the question is: Is there something wrong with those dialogs so they should be avoided? Yes they have (very) limited functionality and customization, but when you don't need anything fancy, is using js dialogs still a bad practice? Why these dialogs haven't seen any improvement in past 10 years (probably longer) and none is planned for near future? Wouldn't it be nice to have native js access to fully customizable desktop-level dialogs? At least adding error/warning/info type of dialogs and adding ability to customize button captions would be a big help.

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  • Python del() built-in can't be used in assignment?

    - by emcee
    I noticed a problem when I was trying to use del in a lambda to thin out a list of threads to just those running: map(lambda x: del(x) if not x.isAlive() else x, self.threads) Ignore for a second that this doesn't do anything, I'm just fooling around with map, reduce, and lambda. This fails with a syntax error at del(x). With some messing around, I think the problem is del() doesn't return a value. For example, this fails with the same error: b = 5 x = del(b) This doesn't, however: def rmThis(x): del(x) Which means I'm using this workaround: map(lambda x: rmThis(x) if not x.isAlive() else x, self.threads) So is the limitation just because del() doesn't return a value? Why not? I'm using python 2.6.2

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  • When should a uniform be used in shader programming?

    - by Phineas
    In a vertex shader, I calculate a vector using only uniforms. Therefore, the outcome of this calculation is the same for all instantiations of the vertex shader. Should I just do this calculation on the CPU and upload it as a uniform? What if I have ten such calculations? If I upload a lot of uniforms in this way, does CPU-GPU communication ever get so slow that recomputing such values in the vertex shader is actually faster?

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  • If I specify a System property multiple times when invoking JVM which value is used?

    - by RobV
    If I specify a system property multiple times when invoking the JVM which value will I actually get when I retrieve the property? e.g. java -Dprop=A -Dprop=B -jar my.jar What will be the result when I call System.getProperty("prop");? The Java documentation on this does not really tell me anything useful on this front. In my non-scientific testing on a couple of machines running different JVMs it seems like the last value is the one returned (which is actually the behavior I need) but I wondered if this behavior is actually defined officially anywhere or can it vary between JVMs?

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  • Port 80 is being used by SYSTEM (PID 4), what is that?

    - by GiH
    I am trying to use port 80 for my application server, but when I perform "netstat -aon" I get TCP 0.0.0.0:80 0.0.0.0:0 LISTENING 4 When I look up the process in task manager, it shows PID 4 is SYSTEM, thats it, not extension... nothing, just "SYSTEM". Whats going on here? I'm afraid to end this process, what do I do? UPDATE: I've solved this through a stackoverflow question. Follow this link to find the solution for how to get IIS to stop listening on port 80 for a specified IP address.

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