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  • Can a loosely typed language be considered true object oriented?

    - by user61852
    Can a loosely typed programming language like PHP be really considered object oriented? I mean, the methods don't have returning types and method parameters has no declared type either. Doesn't class design require methods to have a return type? Don't methods signatures have specifically-typed parameters? How can OOP techniques help you code in PHP if you always have to check the types of parameters received because the language doesn't enforce types? Please, if I'm wrong, explain it to me. When you design things using UML, then code classes in PHP with no return-typed methods and no-type parameters... Is the code really compliant with the UML design? You spend time designing the architecture of your software, then the compiler doesn't force the programmer to follow your design while coding, letting he/she assign any object variable to any other variable with no "type-mismatch" warning.

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  • Type checking and recursive types (Writing the Y combinator in Haskell/Ocaml)

    - by beta
    When explaining the Y combinator in the context of Haskell, it's usually noted that the straight-forward implementation won't type-check in Haskell because of its recursive type. For example, from Rosettacode [1]: The obvious definition of the Y combinator in Haskell canot be used because it contains an infinite recursive type (a = a -> b). Defining a data type (Mu) allows this recursion to be broken. newtype Mu a = Roll { unroll :: Mu a -> a } fix :: (a -> a) -> a fix = \f -> (\x -> f (unroll x x)) $ Roll (\x -> f (unroll x x)) And indeed, the “obvious” definition does not type check: ?> let fix f g = (\x -> \a -> f (x x) a) (\x -> \a -> f (x x) a) g <interactive>:10:33: Occurs check: cannot construct the infinite type: t2 = t2 -> t0 -> t1 Expected type: t2 -> t0 -> t1 Actual type: (t2 -> t0 -> t1) -> t0 -> t1 In the first argument of `x', namely `x' In the first argument of `f', namely `(x x)' In the expression: f (x x) a <interactive>:10:57: Occurs check: cannot construct the infinite type: t2 = t2 -> t0 -> t1 In the first argument of `x', namely `x' In the first argument of `f', namely `(x x)' In the expression: f (x x) a (0.01 secs, 1033328 bytes) The same limitation exists in Ocaml: utop # let fix f g = (fun x a -> f (x x) a) (fun x a -> f (x x) a) g;; Error: This expression has type 'a -> 'b but an expression was expected of type 'a The type variable 'a occurs inside 'a -> 'b However, in Ocaml, one can allow recursive types by passing in the -rectypes switch: -rectypes Allow arbitrary recursive types during type-checking. By default, only recursive types where the recursion goes through an object type are supported. By using -rectypes, everything works: utop # let fix f g = (fun x a -> f (x x) a) (fun x a -> f (x x) a) g;; val fix : (('a -> 'b) -> 'a -> 'b) -> 'a -> 'b = <fun> utop # let fact_improver partial n = if n = 0 then 1 else n*partial (n-1);; val fact_improver : (int -> int) -> int -> int = <fun> utop # (fix fact_improver) 5;; - : int = 120 Being curious about type systems and type inference, this raises some questions I'm still not able to answer. First, how does the type checker come up with the type t2 = t2 -> t0 -> t1? Having come up with that type, I guess the problem is that the type (t2) refers to itself on the right side? Second, and perhaps most interesting, what is the reason for the Haskell/Ocaml type systems to disallow this? I guess there is a good reason since Ocaml also will not allow it by default even if it can deal with recursive types if given the -rectypes switch. If these are really big topics, I'd appreciate pointers to relevant literature. [1] http://rosettacode.org/wiki/Y_combinator#Haskell

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  • Learning to implement dynamic language compiler

    - by TriArc
    I'm interested in learning how to create a compiler for a dynamic language. Most compiler books, college courses and articles/tutorials I've come across are specifically for statically typed languages. I've thought of a few ways to do it, but I'd like to know how it's usually done. I know type inferencing is a pretty common strategy, but what about others? Where can I find out more about how to create a dynamically typed language?

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  • How do you navigate and refactor code written in a dynamic language?

    - by Philippe Beaudoin
    I love that writing Python, Ruby or Javascript requires so little boilerplate. I love simple functional constructs. I love the clean and simple syntax. However, there are three things I'm really bad at when developing a large software in a dynamic language: Navigating the code Identifying the interfaces of the objects I'm using Refactoring efficiently I have been trying simple editors (i.e. Vim) as well as IDE (Eclipse + PyDev) but in both cases I feel like I have to commit a lot more to memory and/or to constantly "grep" and read through the code to identify the interfaces. As for refactoring, for example changing method names, it becomes hugely dependent on the quality of my unit tests. And if I try to isolate my unit tests by "cutting them off" the rest of the application, then there is no guarantee that my stub's interface stays up to date with the object I'm stubbing. I'm sure there are workarounds for these problems. How do you work efficiently in Python, Ruby or Javascript?

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  • New insights I can learn from the Groovy language

    - by Andrea
    I realize that, for a programmer coming from the Java world, Groovy contains a lot of new ideas and cool tricks. My situation is different, as I am learning Groovy coming from a dynamic background, mainly Python and Javascript. When learning a new language, I find that it helps me if I know beforehand which features are more or less old acquaintances under a new syntax and which ones are really new, so that I can concentrate on the latter. So I would like to know which traits distinguish Groovy among the dynamic languages. What are the ideas and insights that a programmer well-versed in dynamic languages should pay attention to when learning Groovy?

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  • Dynamically load and call delegates based on source data

    - by makerofthings7
    Assume I have a stream of records that need to have some computation. Records will have a combination of these functions run Sum, Aggregate, Sum over the last 90 seconds, or ignore. A data record looks like this: Date;Data;ID Question Assuming that ID is an int of some kind, and that int corresponds to a matrix of some delegates to run, how should I use C# to dynamically build that launch map? I'm sure this idea exists... it is used in Windows Forms which has many delegates/events, most of which will never actually be invoked in a real application. The sample below includes a few delegates I want to run (sum, count, and print) but I don't know how to make the quantity of delegates fire based on the source data. (say print the evens, and sum the odds in this sample) using System; using System.Threading; using System.Collections.Generic; internal static class TestThreadpool { delegate int TestDelegate(int parameter); private static void Main() { try { // this approach works is void is returned. //ThreadPool.QueueUserWorkItem(new WaitCallback(PrintOut), "Hello"); int c = 0; int w = 0; ThreadPool.GetMaxThreads(out w, out c); bool rrr =ThreadPool.SetMinThreads(w, c); Console.WriteLine(rrr); // perhaps the above needs time to set up6 Thread.Sleep(1000); DateTime ttt = DateTime.UtcNow; TestDelegate d = new TestDelegate(PrintOut); List<IAsyncResult> arDict = new List<IAsyncResult>(); int count = 1000000; for (int i = 0; i < count; i++) { IAsyncResult ar = d.BeginInvoke(i, new AsyncCallback(Callback), d); arDict.Add(ar); } for (int i = 0; i < count; i++) { int result = d.EndInvoke(arDict[i]); } // Give the callback time to execute - otherwise the app // may terminate before it is called //Thread.Sleep(1000); var res = DateTime.UtcNow - ttt; Console.WriteLine("Main program done----- Total time --> " + res.TotalMilliseconds); } catch (Exception e) { Console.WriteLine(e); } Console.ReadKey(true); } static int PrintOut(int parameter) { // Console.WriteLine(Thread.CurrentThread.ManagedThreadId + " Delegate PRINTOUT waited and printed this:"+parameter); var tmp = parameter * parameter; return tmp; } static int Sum(int parameter) { Thread.Sleep(5000); // Pretend to do some math... maybe save a summary to disk on a separate thread return parameter; } static int Count(int parameter) { Thread.Sleep(5000); // Pretend to do some math... maybe save a summary to disk on a separate thread return parameter; } static void Callback(IAsyncResult ar) { TestDelegate d = (TestDelegate)ar.AsyncState; //Console.WriteLine("Callback is delayed and returned") ;//d.EndInvoke(ar)); } }

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  • Eclipse (Aptana) Typing Lag

    - by Zack
    Hello SO, I've been using Aptana for some time now, and as of recent I've been dealing with files that are really, really big (500+ lines of code, which is huge for me, being a novice developer). Whenever I deal with smaller files, I get that weird sensation that I'm "in front of" what's typing, but now I'm quite sure of it--there is a significant lag between when I type something and when I see the text appear on screen. I don't have this issue with Dreamweaver CS3, so I know my computer has the capability to edit these files without this happening, but Eclipse still lags. I also don't see when something is being deleted if I hold down backspace, I see the first few characters get deleted, but then everything "hangs." Once I release the backspace key, the characters that would've been shown deleting instantly vanish all at once. The same thing happens with the forward delete key. I'm beginning to think this is an issue with Java, since I have the same feeling that everything is slightly "behind me" when I'm using -any- Java application. The computer is an intel Pentium 4 3.2 GHz Prescott, with 2GB's of DDR400 RAM and a Radeon HD3650 graphics card. If anyone knows how to fix this lagging issue, I'm all ears (eyes?); if anyone can recommend a different IDE with capabilities similar to Aptana (I do Python, HTML, CSS and JS; I use Git for SCM), I'd be glad to give it a try. Thanks!

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  • Stop IE users typing into the file upload input

    - by Dexter
    My testers have discovered that if you type free text into a file upload input then none of the buttons on the page work until that text is removed (so the page cannot be submitted). I am able to replicate this with the following ASPX code (with no code behind): <%@ Page Language="C#" AutoEventWireup="true" %> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <body> <form id="form1" runat="server"> <div> <asp:FileUpload ID="fuTest" runat="server" /> <asp:Button ID="btnSubmit" runat="server" Text="Submit" /> </div> </form> </body> </html> (Note that I haven't bound any handlers to the page; despite this, the page is submitted when the submit button is clicked only if no text is entered into the upload text box) Is there any way to prevent users from typing free text into a file upload control? It seems that this is only possible in IE - Firefox and Chrome natively prevent text from being entered into upload input fields. I've seen solutions elsewhere which suggest hiding input and replacing it with a label / button combo, but this seems like it might cause more problems and work inconsistently across browsers. Any thoughts?

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  • How to use setTimeout / .delay() to wait for typing between characters

    - by Darcy
    Hi all, I am creating a simple listbox filter that takes the user input and returns the matching results in a listbox via javascript/jquery (roughly 5000+ items in listbox). Here is the code snippet: var Listbox1 = $('#Listbox1'); var commands = document.getElementById('DatabaseCommandsHidden'); //using js for speed $('#CommandsFilter').bind('keyup', function() { Listbox1.children().remove(); for (var i = 0; i < commands.options.length; i++) { if (commands.options[i].text.toLowerCase().match($(this).val().toLowerCase())) { Listbox1.append($('<option></option>').val(i).html(commands.options[i].text)); } } }); This works pretty well, but slows down somewhat when the 1st/2nd char's are being typed since there are so many items. I thought a solution I could use would be to add a delay to the textbox that prevents the 'keyup' event from being called until the user stops typing. The problem is, I'm not sure how to do that, or if its even a good idea or not. Any suggestions/help is greatly appreciated.

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  • Custom android preference type loses focus when typing

    - by Brian
    I created a simple preference class that shows an AutoCompleteTextView control and it displays properly but when i focus on the AutoCompleteTextView and start typing it brings up the keyboard but then immediately loses focus on the control. Any idea why this loses focus? Here's what i did to create the view. the inflated layout is just a basic linear layout with a title textview in it. I could change it to a dialog preference instead I guess but it'd be smoother if it could be part of the base view. @Override protected View onCreateView(ViewGroup parent) { LayoutInflater inflater = (LayoutInflater) getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE); LinearLayout layout = (LinearLayout) inflater.inflate(R.layout.base_preference, null); if (mHint != null) { TextView hintView = (TextView) layout.findViewById(R.id.PreferenceHintTextView); hintView.setText(mHint); } TextView titleView = (TextView) layout.findViewById(R.id.PreferenceTitleTextView); titleView.setText(getTitle()); AutoCompleteTextView inputView = new AutoCompleteTextView(getContext()); inputView.setGravity(Gravity.FILL_HORIZONTAL); ArrayAdapter<CharSequence> adapter = new ArrayAdapter<CharSequence>(getContext(), R.layout.auto_complete_text_list_item, getEntries()); inputView.setAdapter(adapter); inputView.setThreshold(1); inputView.setOnItemSelectedListener(this); layout.addView(inputView); return layout; }

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  • Format textfield while typing Ios

    - by BBios
    Ive seen other examples and tried - (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string I am not sure what I am doing wrong, I just started coding my first Iphone App This is what I am trying to do I have 4 textfields and each has a limit on number of letters while typing I have done this using the below code - (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string { int valid; NSString *cs2 = [textField.text stringByReplacingCharactersInRange:range withString:string]; // int charCount = [cs2 length]; if(textField == cvv){ valid = 4; }else if(textField == cardName) { valid=26; }else if(textField == expDate) { valid=5; // if (charCount == 2 ) { // textField.text = [cs2 stringByAppendingString:@"/"]; // textField.text = cs2; // return YES; // } }else if(textField == acNumber) { valid=19; } return !([cs2 length] > valid); Works fine till here, I have a textfield where the user enters Exp date and would like to format it as if I am entering 112 then it should display as 01/12 and if I enter 2 then it should display as 1122 I tried checking if the length of the textfield value is 2 then append a / but then that gives me when I enter 12 it gives 11/22

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  • wcf rest service 400 error : There might be a typing error in the address

    - by Lokesh Kondapalli
    I am trying to invoke wcf rest service from url but its showing error like this Error : Most likely causes: •There might be a typing error in the address. •If you clicked on a link, it may be out of date. ** I need JSON responce Here my code : Iservice.cs using System; using System.Collections.Generic; using System.Linq; using System.Runtime.Serialization; using System.ServiceModel; using System.ServiceModel.Web; using System.Text; namespace SampleRestSample { interface name "IService1" in both code and config file together. [ServiceContract] public interface IService1 { [OperationContract] [WebInvoke(Method = "GET", UriTemplate = "Book/{id}", BodyStyle = WebMessageBodyStyle.Wrapped, ResponseFormat = WebMessageFormat.Json)] List<Prasad> GetBookById(string id); } [DataContract] public class Prasad { [DataMember] public string Name { get; set; } [DataMember] public string Age { get; set; } } } Service1.svc.cs using System; using System.Collections.Generic; using System.Linq; using System.Runtime.Serialization; using System.ServiceModel; using System.ServiceModel.Web; using System.Text; namespace LoginRestSample { // NOTE: You can use the "Rename" command on the "Refactor" menu to change the class name "Service1" in code, svc and config file together. public class Service1 : SampleRestSample { List<Prasad> list = new List<Prasad>(); public List<Prasad> GetBookById(string id) { try { Prasad cls = new Prasad(); cls.Age = "24"; cls.Name = "prasad"; list.Add(cls); //int bookId = Convert.ToInt32(id); //using (SampleDbEntities entities = new SampleDbEntities()) //{ // return entities.Books.SingleOrDefault(book => book.ID == bookId); //} } catch { throw new FaultException("Something went wrong"); } return list; } } } web.config <?xml version="1.0" encoding="utf-8"?> <configuration> <system.web> <compilation debug="true" targetFramework="4.0"> <assemblies> <add assembly="System.Data.Entity, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" /> </assemblies> </compilation> </system.web> <system.serviceModel> <services> <service name="WcfRestSample.SampleRestSample"> <endpoint address="" behaviorConfiguration="restfulBehavior" binding="webHttpBinding" bindingConfiguration="" contract="WcfRestSample.ISampleRestSample" /> <host> <baseAddresses> <add baseAddress="http://localhost/SampleRestSample" /> </baseAddresses> </host> </service> </services> <behaviors> <endpointBehaviors> <behavior name="restfulBehavior"> <webHttp automaticFormatSelectionEnabled="true" /> </behavior> </endpointBehaviors> <serviceBehaviors> <behavior name=""> <serviceMetadata httpGetEnabled="true" /> <serviceDebug includeExceptionDetailInFaults="false" /> </behavior> </serviceBehaviors> </behaviors> <serviceHostingEnvironment multipleSiteBindingsEnabled="true" /> </system.serviceModel> <system.webServer> <modules runAllManagedModulesForAllRequests="true" /> </system.webServer> </configuration> Any solutions? Thank you in advance.

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  • learning to type - tips for programmers?

    - by OrbMan
    After hunting and pecking for about 35 years, I have decided to learn to type. I am learning QWERTY and have learned about 2/3 of the letters so far. While learning, I have noticed how asymmeterical the keyboard is, which really bothers me. (I will probably switch to a symmetrical keyboard eventually, but for now am trying to do everything as standard and "correct" as possible.) Although I am not there yet in my lessons, it seems that many of the keys I am going to use as a C# web developer are supposed to be typed by the pinky of my right hand. Are there any typing patterns you have developed that are more ergonomic (or faster) when typing large volumes of code rife with braces, colons, semi-colons and quotes? Or, should I just accept the fact that every other key is going to be hit with my right pinky? It is not that speed is such a huge concern, as much as that it seems so inefficient to rely on one finger so much... As an example, some of the conventions I use as a hunt and pecker, like typing open and close braces right away with my index and middle finger, and then hitting the left arrow key to fill in the inner content, don't seem to work as well with just a pinky. What are some typing patterns using a standard QWERTY keyboard that work really well for you as a programmer?

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  • Switch to tab by typing a substring of its name in Visual Studio 2005

    - by Vineus
    Is there a way to navigate between tabs in VS similar to the emacs iswtichb-mode or Firefox ubiquity switch tab mode (https://wiki.mozilla.org/Labs/Ubiquity/Ubiquity_0.1_Author_Tutorial#Switching_Tabs) ? In these apps, you just type a substring of the title of the tab (or buffer for emacs) to switch to this tab. For instance, to switch to a tab named "App_Code/Data/MyProgram.cs", you just invoke the tab switching command and then type "Progr" for instance to list all the tab whose name matches this string, including "MyProgram.cs". It's much easier to switch between tabs this way when you have a lot of documents open and when you now where to go (which is the case in most situation) Thank you !

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  • MVC2 Strong typing breaking changes...

    - by BitFiddler
    I had the code working for: http://stackoverflow.com/questions/1930229/post-idictionary-back-to-mvc-model I recently migrated to MVC2 and now all my collections/dictionaries are coming back null. I can't seem to find any information about what has changed in the new release to cause this. Anyone know of something that might help?

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  • Why do properties require explicit typing during compilation?

    - by ctpenrose
    Compilation using property syntax requires the type of the receiver to be known at compile time. I may not understand something, but this seems like a broken or incomplete compiler implementation considering that Objective-C is a dynamic language. The property "comment" is defined with: @property (nonatomic, retain) NSString *comment; and synthesized with: @synthesize comment; "document" is an instance of one of several classes which conform to: @protocol DocumentComment <NSObject> @property (nonatomic, retain) NSString *comment; @end and is simply declared as: id document; When using the following property syntax: stringObject = document.comment; the following error is generated by gcc: error: request for member 'comment' in something not a structure or union However, the following equivalent receiver-method syntax, compiles without warning or error and works fine, as expected, at run-time: stringObject = [document comment]; I don't understand why properties require the type of the receiver to be known at compile time. Is there something I am missing? I simply use the latter syntax to avoid the error in situations where the receiving object has a dynamic type. Properties seem half-baked.

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  • Don't understand the typing of Scala's delimited continuations (A @cps[B,C])

    - by jkff
    I'm struggling to understand what precisely does it mean when a value has type A @cps[B,C] and what types of this form should I assign to my values when using the delimited continuations facility. I've looked at some sources: http://lamp.epfl.ch/~rompf/continuations-icfp09.pdf http://www.scala-lang.org/node/2096 http://dcsobral.blogspot.com/2009/07/delimited-continuations-explained-in.html http://blog.richdougherty.com/2009/02/delimited-continuations-in-scala_24.html but they didn't give me much intuition into this. In the last link, the author tries to give an explicit explanation, but it is not clear enough anyway. The A here represents the output of the computation, which is also the input to its continuation. The B represents the return type of that continuation, and the C represents its "final" return type—because shift can do further processing to the returned value and change its type. I don't understand the difference between "output of the computation", "return type of the continuation" and "final return type of the continuation". They sound like synonyms.

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  • Static Typing and Writing a Simple Matrix Library

    - by duckworthd
    Aye it's been done a million times before, but damnit I want to do it again. I'm writing a simple Matrix Library for C++ with the intention of doing it right. I've come across something that's fairly obvious in mathematics, but not so obvious to a strongly typed system -- the fact that a 1x1 matrix is just a number. To avoid this, I started walking down the hairy path of matrices as a composition of vectors, but also stumbled upon the fact that two vectors multiplied together could either be a number or a dyad, depending on the orientation of the two. My question is, what is the right way to deal with this situation in a strongly typed language like C++ or Java?

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  • c# scope/typing/assignment question

    - by Shannow
    Hi there another quick question. I would like to create a variable object so that depending on the value of something, it gets cast as needed. e.g. var rule; switch (seqRuleObj.RuleType) { case SeqRuleObj.type.Pre : rule = new preConditionRuleType(); rule = (preConditionRuleType)seqRuleObj.Rule; break; case SeqRuleObj.type.Post : rule = new postConditionRuleType(); rule = (postConditionRuleType)seqRuleObj.Rule; break; case SeqRuleObj.type.Exit : rule = new exitConditionRuleType(); rule = (exitConditionRuleType)seqRuleObj.Rule; break; default : break; } String result; foreach (sequencingRuleTypeRuleConditionsRuleCondition cond in rule.ruleConditions.ruleCondition) { ....../ blah } so basically this will not work. c# will not allow me to create an new object in every case as the name is aleady defined. i can just paste the foreach loop into each case but that to me is such a waste, as the objects are exactly the same in all but name.

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  • Can jQuery add commas while user typing numbers?

    - by Matt
    How would I go about dynamically adding commas as a user is entering numbers? Is there a good number formatter that would help? I have to add these numbers later so I eventually have to remove the commas down the line. But the screen needs to show the commas for better readability.

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  • scroll/search JList when user starts typing

    - by alex
    I would like to implement one of the fanciest features I every now and then. I would like to allow a user to click on a JList and if words are typed, do a query and advance the caret to the next match (prefix). Is there and example of such an implementation in Java somewhere? I'm thinking a combination of key listeners, getNextMatch() and setSelectValue().

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  • Typing enter/return key in selenium

    - by Nathan
    Looking for a quick way to type an enter or return key in Selenium. Unfortunately the form I'm trying to test (not my own code so I can't modify) doesn't have a submit button. When working with it manually, I just type enter or return, and just need to know how to do that with the Selenium "type" command

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  • how to userinput without typing to a batch file

    - by Blood hound
    I am trying to run a batch file which requires user input "y/n" to do further action , I want to call this batch file for automation , as during automation argument yes or no need to be passed without user intervention , any idea how to achieve it ? cmd /c setup.bat now if setup.bat is run " yes or no " need to be selected to get the desired result as now this setup.bat is called during automation, is there is anyway to pass "yes" parameter as an input to setup.bat

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  • Typing Text effect not working

    - by Anthony Garand
    I'm writing a script to take an array of strings, split them by characters, and print them out to the screen. This is what I have and for some reason it is not doing anything. Any ideas? function autowrite() { var write_text=["Your Memories","Your Thoughts","Your Photos"]; var split_text = Array(); var i; var c; for(i=0; i < write_text.length; i++) { split_text[i] = write_text[i].split(""); for(c=0; i < split_text.length[i]; i++) { alert(split_text[i][c]); } } }

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