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  • How do I indicate that a class doesn't support certain operators?

    - by romeovs
    I'm writing a class that represents an ordinal scale, but has no logical zero-point (eg time). This scale should permit addition and substraction (operator+, operator+=, ...) but not multiplication. Yet, I always felt it to be a good practice that when one overloads one operator of a certain group (in this case the math operators), one should also overload all the others that belong to that group. In this case that would mean I should need to overload the multiplication and division operators also, because if a user can use A+B he would probable expect to be able the other operators. Is there a method that I can use to throw an error for this at compiler time? The easiest method would be just no to overload the operators operator*, ... yet it would seem appropriate to add a bit more explaination than operator* is not know for class "time". Or is this something that I really should not care about (RTFM user)?

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  • How to design desktop app ? (from web app dev)

    - by Henry
    I have only worked on web apps for my whole career. I'm starting a new desktop (Adobe AIR) app project but I found myself having difficulties with: stuck with thinking about overall UI design in the traditional page model not sure how to handle the navigation part in the UI not taking advantage of states deciding what should be implemented on client vs server side. Any advice? Thanks.

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  • How to map non-REST URLS to REST ones?

    - by Krzysztof Luks
    I have a small rails app that has default scaffold generated routes eg. /stadia/1.xml. However I have to support legacy client app that can't construct such URLs correctly. What I need to do is to map URL in the form: /stadia?id=1?format=xml to /stadia/1.xml Or even something like: /myApp?model=<model_name>?id=<id>?format=xml to /<model_name/<id>.xml Is it possible to craft appropriate route in Rails?

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  • Find a regular expression that matches a string?

    - by Mirai
    I need a model for finding all of the regular expressions that would match a particular string. Basically, I need an algorithm for doing what I do to generate a regex search string from some pattern. My purpose for this to create a list of potential regular expressions from a selection of text and order that list from least specific (i.e. string of characters with abitrary length) to most specific (i.e. the string itself) to be used in text editor.

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  • question and answer engine architecture

    - by sarvesh
    Can anyone give me insights as to how websites like chacha.com / kgb.com are designed. What could be the components involved when a user sends out an sms and how is that question stored. Should the question and answers be stored in a relational model or non relational?

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  • Checking an empty Core Data relationship (SQLite)

    - by rwat
    I have a to-many relationship in my data model, and I'd like to get all the objects that have no corresponding objects in the relationship. For example: Customer - Purchases I want to get all Customers that have 0 Purchases. I've read somewhere that I could use "Purchases[SIZE] = 0", but this gives me an unsupported function expression error, which I think means it doesn't work with a SQLite backing store (which I don't want to switch from, due to some performance constraints). Any ideas?

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  • In R, how do you get the best fitting equation to a set of data?

    - by Matherion
    I'm not sure wether R can do this (I assume it can, but maybe that's just because I tend to assume that R can do anything :-)). What I need is to find the best fitting equation to describe a dataset. For example, if you have these points: df = data.frame(x = c(1, 5, 10, 25, 50, 100), y = c(100, 75, 50, 40, 30, 25)) How do you get the best fitting equation? I know that you can get the best fitting curve with: plot(loess(df$y ~ df$x)) But as I understood you can't extract the equation, see Loess Fit and Resulting Equation. When I try to build it myself (note, I'm not a mathematician, so this is probably not the ideal approach :-)), I end up with smth like: y.predicted = 12.71 + ( 95 / (( (1 + df$x) ^ .5 ) / 1.3)) Which kind of seems to approximate it - but I can't help to think that smth more elegant probably exists :-) I have the feeling that fitting a linear or polynomial model also wouldn't work, because the formula seems different from what those models generally use (i.e. this one seems to need divisions, powers, etc). For example, the approach in Fitting polynomial model to data in R gives pretty bad approximations. I remember from a long time ago that there exist languages (Matlab may be one of them?) that do this kind of stuff. Can R do this as well, or am I just at the wrong place? (Background info: basically, what we need to do is find an equation for determining numbers in the second column based on the numbers in the first column; but we decide the numbers ourselves. We have an idea of how we want the curve to look like, but we can adjust these numbers to an equation if we get a better fit. It's about the pricing for a product (a cheaper alternative to current expensive software for qualitative data analysis); the more 'project credits' you buy, the cheaper it should become. Rather than forcing people to buy a given number (i.e. 5 or 10 or 25), it would be nicer to have a formula so people can buy exactly what they need - but of course this requires a formula. We have an idea for some prices we think are ok, but now we need to translate this into an equation.

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  • WM_SYSCOMMAND oddities

    - by Andreas Rejbrand
    An application recieves the WM_SYSCOMMAND message when the user selects a menu item command on the system menu, and so wParam can be SC_CLOSE, SC_CONTEXTHELP, SC_MAXIMIZE, SC_MINIMIZE, SC_RESTORE etc. That's logical. But one can also send the WM_SYSCOMMAND message to send commands to the Windows Shell. For instance, one can display the start menu (SC_TASKLIST), activate the screen saver (SC_SCREENSAVE), and turn off the monitor (SC_MONITORPOWER). This does not make sense, does it? What does this have to do with the application's system menu? This is more of a "system command", i.e. more of a completely other interpretation of the name "WM_SYSCOMMAND" of the message. It's like the message is used to send command requests to the system. Why is this message used for two seemingly entirely different things, and what thing does the name "SYSCOMMAND" refer to (command on the system menu, or command of the operating system)?

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  • SQL Server JOIN with optional NULL values

    - by Paul McLoughlin
    Imagine that we have two tables as follows: Trades ( TradeRef INT NOT NULL, TradeStatus INT NOT NULL, Broker INT NOT NULL, Country VARCHAR(3) NOT NULL ) CTMBroker ( Broker INT NOT NULL, Country VARCHAR(3) NULL ) (These have been simplified for the purpose of this example). Now, if we wish to join these two tables on the Broker column, and if a country exists in the CTMBroker table on the Country, we have the following two choices: SELECT T.TradeRef,T.TradeStatus FROM Trades AS T JOIN CTMBroker AS B ON B.Broker=T.Broker AND ISNULL(B.Country, T.Country) = T.Country or SELECT T.TradeRef,T.TradeStatus FROM Trades AS T JOIN CTMBroker AS B ON B.Broker=T.Broker AND (B.COUNTRY=T.Country OR B.Country IS NULL) These are both logically equivalent, however in this specific circumstance for our database (SQL Server 2008, SP1) two different execution plans are produced for these two queries with the second version significantly outperforming the first version in terms of both time and logical reads. My question really is as follows: as a general rule would (2) be preferred to (1), or does this just happen to be exploiting some particular idiosyncracy of the optimiser in 2008 SP1 (that could therefore change with future versions of SQL Server).

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  • Returning modified data to a template

    - by Duncan
    I need to amend QuerySet data when i return it to a template. for example, model.objects.all() returns a date (with other fields), but i also want to return the number of days since that date has passed. This is so that in the template, i can say "you last logged in 4 days ago". What is the best way to do this?

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  • Authlogic's current_user object in models

    - by jriff
    Hi all! I need to know the ID of the current user in a model: def after_save desc, points=nil, nil if answer_index == daily_question.correct_answer_index desc = I18n.t('daily_question.point_log.description.correct') points=daily_question.points else desc = I18n.t('daily_question.point_log.description.incorrect') end current_user.give_points(:description => desc, :points => points ) end But I guess that is not how it is done? Regards, Jacob

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  • What types of objects should the ViewModel reference in the MVVM pattern?

    - by Blanthor
    I've seen quite a few examples of MVVM. I can see that the View should reference the ViewModel. I've seen recently an example of a ViewModel referencing a View, which seems wrong to me, as it would result in tighter coupling. Given that ViewModel is often described as an intermediary between the View and the Model, is there more to the ViewModel than a facade to domain objects? I hope I used the term "facade" correctly here.

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  • Where is the best place to put <script> tags in HTML markup?

    - by mipadi
    When embedding JavaScript in an HTML document, where is the best place to put the <script> tags and included JavaScript? I seem to recall that you are not supposed to place these in the <head> section, but placing at the beginning of the <body> section is bad, too, since the JavaScript will have to be parsed before the page is rendered completely (or something like that). This seems to leave the end of the <body> section as a logical place for <script> tags. So, where is the best place to put the <script> tags? (This question references this question, in which it was suggested that JavaScript function calls should be moved from <a> tags to <script> tags. I'm specifically using JQuery, but more general answers are also appropriate.)

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  • Function chaining depending on boolean result

    - by Markive
    This is just an efficiency question really.. I'm interested to know if there is a more efficient or logical way that people use to handle this sort of scenario. In my asp.net application I am running a script to generate a new project my code at the top level looks like this: Dim ok As Boolean = True ok = createFolderStructure() If ok Then ok = createMDB() If ok Then ok = createProjectConfig() If ok Then ok = updateCompanyConfig() I create a boolean and each function returns a boolean result, the next function in this chain will only run if the previous one was successful. I do this because an asp.net application will continue to run through the page life cycle unless there is an unhandled exception and I don't want my whole application to be screwed up if something in the chain goes wrong (there is a lot of copying and deleting of files etc.. in this example). I was just wondering how other people handle this scenario? the vb.net single line if statement is quite succinct but I'm wondering if there is a better way?

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  • Is there an ActiveRecord equivalent to using a nested subquery i.e. ... where NOT IN(select...) ?

    - by Snorkpete
    I have 3 models: Category, Account, and SubAccount The relations are: Accounts has_many :sub_accounts Categories has_many :sub_accounts I wanted to get a list of all Categories that are not used by a given account. My method in the Category model currently looks like: class Category < ActiveRecord::Base def self.not_used_by(account) Category.find_by_sql("select * from categories where id not in(select category_id from sub_accounts where account_id = #{account.id})") end end My question is, is there a cleaner alternative than using SQL? NB. I am currently using Rails 3(beta)

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  • How can I upload and parse a vcard using ruby on rails?

    - by Angela
    I would like to be able to upload a vcard and have it parsed into my application's Model. I am thinking that Paperclip would be a way to upload, but I have no idea how to do the parse. I did a search on google, the only library that seems related is vpim, with mixed commentary. Wanted to see what brilliant ideas might be out there to solve this...thanks.

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  • How to refresh the textbox text when tabs are Changed in WPF

    - by StonedJesus
    Well in my WPF application I am using Tab Control which has around 5 tabs. The view of each tab is a user control which I add via a tool box. Main Xaml File: <Grid> <TabControl Height="Auto" HorizontalAlignment="Stretch" Margin="0" Name="tabControl1" VerticalAlignment="Stretch" Width="Auto"> <TabItem Header="Device Control" Name="Connect"> <ScrollViewer Height="Auto" Name="scrollViewer1" Width="Auto"> <my:ConnectView Name="connectView1" /> </ScrollViewer> </TabItem> <TabItem Header="I2C"> <ScrollViewer Height="Auto" Name="scrollViewer2" Width="Auto"> <my1:I2CControlView Name="i2CControlView1" /> </ScrollViewer> </TabItem> <TabItem Header="Voltage"> <ScrollViewer Height="Auto" Name="scrollViewer3" Width="Auto"> <my2:VoltageView Name="voltageView1" /> </ScrollViewer> </TabItem> </TabControl> </Grid> If you notice each view ie.e Connect, I2C and Voltage is a user control which has a view, viewmodel and model class :) Each of these views have set of textboxes in their respective xaml files. Connect.xaml: <Grid> <Textbox Text="{Binding Box}", Name="hello" /> // Some more textboxes </Grid> I2c.xaml: <Grid> <Textbox Text="{Binding I2CBox}", Name="helI2c" /> // Some more textboxes </Grid> Voltage.xaml: <Grid> <Textbox Text="{Binding VoltBox}", Name="heVoltllo" /> // Some more textboxes </Grid>** By default I have set the text of these textboxes to some value. Lets say "12" "13" "14" respectively in my view model classes. My main requirement is to set the text of these textboxes present in each user control to get refreshed when I change the tab. Description: Lets say Connect View is displayed: Value of Textbox is 12 and I edit it and change it to 16. Now I click on I2C tab and then I go back to Connect tab, I want the textbox value to get refreshed back to the initial value i.e. 12. To be precise, is their a method called visibilitychanged() which I can write in all my user control classes, where I can set the value of these Ui components whenever tabs are changed? Please help :)

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  • Any PHP MVC framework planning to use 5.3 features?

    - by alexandrul
    I would like to get started with PHP, and 5.3 release seems to bring many nice features (namespaces, lambda functions, and many others). I have found some MVC frameworks, and some of them support only PHP 5: PHP Frameworks PHP MVC Frameworks Model–view–controller on Wikipedia but can anyone recommend one of those MVC frameworks that plans to actively use PHP 5.3 features, not just being compatible with PHP 5.3? Update Results so far: Zend Framework 2.0 (in development) Lithium (in development, based on CakePHP) Symfony (in development) FLOW3 (in development, alpha)

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