Matt Manela's Blog

How to teach your girlfriend Hexadecimal?

MattManela — Wed, 06 May 2009 23:49:00 GMT

It is an age old question: How do you teach your girlfriend hex?

I encountered this problem when I was a web developer in college for a late night student activities program aptly named Late Nite Binghamton. My co-worker and girlfriend Mallory was a graduate assistant for the program and had many ideas for how to make the website better and more engaging. While working with her she would often see me typing in the hexadecimal color codes in css such as:

color: #F24A7D

As I am inept with what color look good (I often say that I never learnt colors) I would often ask her for help with picking out colors and I decided that if she was able to give me these colors in their hex color codes it would make us more efficient :) I sat her down and described to her how they work but after talking for a bit I realized that although she understood everything that I said she wouldn’t gain a feel for what hex numbers related to what colors just from hearing me talk.

In order to help her gain this feel I created a simple game called The Mallory Color Guessing Game. The game is a webpage which shows you a large colored box and it is your job to guess what the hex color code is.

After you guess it tells you how close you were to the actual color:

This game was a hit! Mallory loved it and she would compete with me to see who could guess the color the best. Pretty quickly she gained a feel for what the hex digits meant and what color they represented. And that is how I taught my girlfriend hex!

NOTE: Mallory consistently gets over 80% at the Msllory Color Guessing Game.

Snippet Designer in April’s MSDN Magazine!

MattManela — Tue, 14 Apr 2009 23:33:47 GMT

I am excited to announce that the Snippet Designer is featured in the April issue of MSDN Magazine.

It is featured in the Toolbox column where they highlight useful tools and blogs. Here is a snippet of what it says:

Creating Code Snippets is a lot easier when using Snippet Designer (version 1.1), a free, open-source Add-In for Visual Studio 2008 for creating and editing Code Snippets directly within the IDE. Once you install it, creating a new Code Snippet is as easy as going to the File menu and creating a new Code Snippet File.

That is so cool! If you are interested go and download the Snippet Designer from the Codeplex website and give me more feedback.

Also, in the same article my friend Sara Ford had her blog featured. When I found out the Snippet Designer and Sara’s blog were in the magazine I quickly emailed to ask Sara if she knew about it. She already did and also had an extra copy of the magazine for me!

A functional take on console program loop in F#

MattManela — Tue, 14 Apr 2009 04:51:19 GMT

Often when learning a new technology I start with a simple console application in which the program is run in a loop it continues to prompt you for more input until you give some command like quit or exit or whatever you choose:

Enter input: someInput
someOutput
Enter input: otherInput
someoutPut
Enter input: quit
Thanks! Come again!

The code for this is in an imperative language is usually something like:

       1: while(true)

       2: {

       3:     Console.Write("\nEnter input:");

       4:     var line = Console.ReadLine();

       5:     if(line == "quit") break;

       6:     

       7:     doSomething(line);

       8: }

       9:  

      10: Console.WriteLine("Thanks! Come Again");

While reading some F# samples, I saw some code doing essentially the same thing which looked something like:

       1: Console.Write "\nEnter input:"

       2: let mutable input = Console.ReadLine()

       3: while input <> "quit"

       4:     do

       5:     

       6:     if input <> "quit" 

       7:     then

       8:         doSomething input

       9:         Console.Write "\nEnter input:" 

      10:         input <- Console.ReadLine()

Now this just feels dirty! In a functional language explicit loop constructs like a while loop feel wrong. I different way of doing this which is more functional is to create an infinite list of actions. Where each action represents one iteration of any of the above loops. Then you just execute each action until some condition is met (like seeing the input “quit”).

       1: let action = fun _ ->

       2:     Console.Write "\nEnter input: "

       3:     Console.ReadLine()

       4:  

       5: let readlines = Seq.init_infinite (fun _ -> action())

       6:     

       7: let run item = if item = "quit" 

       8:                 then Some(item) 

       9:                 else

      10:                     parse item 

      11:                     None

      12:  

      13: Seq.first run readlines |> ignore

      14: Console.WriteLine "Thanks! Come Again"

This code makes use of the Seq.init_infinite which create a infinite sequence and Seq.first which enumerates the sequence until the passed in function returns Some.

Synchronizing Scrollbars using JQuery

MattManela — Thu, 19 Mar 2009 20:29:11 GMT

I just wrote this simple plugin for JQuery which lets you synchronize the scroll bars of any collection of elements. This lets you move the scrollbar of one div it have the scrollbars’ of the rest of the divs move the same exact amount.

Here is the code:

        1: jQuery.fn.synchronizeScroll = function() {

       2:  

       3:            var elements = this;

       4:            if (elements.length <= 1) return;

       5:  

       6:            elements.scroll(

       7:            function() {

       8:                var left = $(this).scrollLeft();

       9:                var top = $(this).scrollTop();

      10:                elements.each(

      11:                function() {

      12:                    if ($(this).scrollLeft() != left) $(this).scrollLeft(left);

      13:                    if ($(this).scrollTop() != top) $(this).scrollTop(top);

      14:                }

      15:                );

      16:            });

      17:        }

Using this is SUPER simple. Lets say you have several divs defined as:

<div class=”scrollDiv” style=”overflow:auto;”> .. some large content</div>

To synchronize the scrollbars’ on all divs with the class scrollDiv all you need to write is:

$(“.scrollDiv”).synchronizeScroll();

Prime Factorization using Unfold in Haskell

MattManela — Tue, 17 Mar 2009 13:53:00 GMT

I randomly yesterday started thinking about the unfoldr function in Haskell while working out at the gym (how nerdy is that, I am lifting iron but thinking of functional programming). Unfoldr take a single and an unfolding function and turns it into a list (the opposite of fold). At the gym I was thinking about an application where I can use this and I decided that when I got home I would use it to write a prime factorization function. This is a method that when given a number returns the list of its prime factors.

It was easy to write the only part I am not pleased about is the code I used to deal with tuples. It seems clumsy and I am still looking for a way to clean that up.

One note: The code below references a list of prime numbers called primes , which is not shown.

Here is the code:

   1: primeFactors x = unfoldr findFactor x   2:                  where   3:                    first (a,b,c) = a   4:                    findFactor 1 = Nothing   5:                    findFactor b = (\(_,d,p)-> Just (p, d))   6:                                   $ head $ filter ((==0).first)    7:                                   $  map (\p -> (b `mod` p, b `div` p, p))  primes

This function will take any number which is greater than 1 and return a list of its prime factors. But don’t take my word for it, I wrote a quickcheck property to ensure the prime factors multiply back to the original number:

   1: prop_factors num =  num > 1 ==> num == (foldr1 (*) $ primeFactors num)

When running quickcheck on this property you see the following:

quickCheck prop_factors
OK, passed 100 tests.

My xUnit.net Visual Studio Code Snippets

MattManela — Mon, 02 Mar 2009 23:58:00 GMT

The xUnit .Net codeplex page lists one useful Visual Studio code snippet for creating a Fact. As you can tell I am fairly fond of code snippets so I created a few more which I use when writing xUnit.net facts. These are one line snippets that I find very convenient when writing my assertions.

Below is a table which shows the shortcut you use to access the snippet and the code the snippet generates

Shortcut	Snippet
ae	Assert.Equal($expected$,$actual$)
ane	Assert.NotEqual($expected$,$actual$)
an	Assert.Null($actual$)
ann	Assert.NotNull($actual$)
at	Assert.True($actual$)
af	Assert.False($actual$)

I have included a zip containing these snippets. Enjoy!

Code Assumptions

MattManela — Mon, 02 Feb 2009 04:13:42 GMT

My co-workers and I recently came across a piece of code which exposed some assumptions we had about the “correct” behavior of two functions; these assumptions turned out to be false. The code dealt with determining if the IP of a request coming into to a website matches a certain range of IP address. The range of IP address was defined in a config file and could look something like this:

156.27.1.2, 156.*.*.*, 127.0.0.*

Where the * acts as a wild card and each comma-separated IP format is matched against the incoming IP address. The code’s intended behavior is that specifying no IP address formats in the config would mean that no IP addresses would match the format. We noticed that this wasn’t holding true. We went to examine the code that was performing the matching (which none of us had written and sadly has NO test cases around it). The code boiled down to something like this:

        1: bool DoesIPMatchIPFormat(string incomingIpAddress, string ipFormatsFromConfig)

       2: {

       3:     foreach(var ipFormat in ipFormatsFromConfig.Split(','))

       4:     {

       5:         Regex re = ConvertFormatIntoRegex(ipFormat);

       6:         if(rs.Match(incomingIpAddress).Success) return true;

       7:     }

       8: }

Where ipFormatsFromConfig is the ip range of formats shown above separated by “,” or an empty string if no formats are given. On first glance we all were confused by why this didn’t work and then as we looked into it we realized we had made some incorrect assumptions.

First, we assumed that “”.Split(‘,’) would return a zero element array. This assumption is false. It returns a 1 element array containing the empty string.

After we learned this we encountered our second assumption. We assumed that a regular expression whose pattern was an empty string would not match anything. (ConvertFormatIntoRegex returned just that). This assumption is also false. After learning the true behavior, it makes sense why it behaves this way. (A DFA with only one state must accept every input. )

Our assumptions about the “correct” behavior of functions reflect similar mistakes made by all programmers; assuming that you don’t make these kinds of assumptions is a very dangerous way to program and reinforces the importance of unit testing.

Snippet Designer 1.1 Released

MattManela — Tue, 06 Jan 2009 02:11:28 GMT

I just released Snippet Designer 1.1. This is not a major release but just some bug fixes and often requested changes to make the snippet designer more useful.

Some of the most notable changes are:

Languages Service are turned OFF by default now. Since I was unable to figure out a way to host the C# and VB language services in the snippet editor without causing fake errors in projects I decided to give the users an option to turn them on or off. If you are ok with the fake error you can turn this back on but since it really annoyed me I have it off. I plan in a future release to provide some basic color coding outside of the language service so you can at least have color coded code.
Many more aspects of the plug in are now configurable through the options menu under Snippet Designer. you can now set the location of the snippet index, set preferences for which snippet languages you would like to appear in the snippet explorer.
Several bug fixes to how the highlighting of replacements works and performance improvements with it also.

Hopefully these changes will make it much more useful so please download it and try it out here.

The future…

My plans for the future are still up in the air but some of the things I would like to add are:

More bug fixes and more feature enhancements suggested by many helpful users on the Snippet Designer Codeplex page.
Ability to color code snippets without using the language service. I have a few options here I have been looking at.
Create a website to host snippets and allow you to consume and publish from Visual Studio to this website.

I don’t know how much time I will have to commit to any of these but hopefully I will be able to get more work done on this.

Thanks!

Inline Regular Expression Options

MattManela — Thu, 01 Jan 2009 20:10:15 GMT

I was using attributes from the System.ComponentModel.DataAnnotations namespace for model validation. This namespace includes a few very useful validation attributes such as

Required Attribute – Validates the field has a value
Range Attribute – Validates the field is within a given range
RegularExpression Attribute – Validates the field matches a given regular expression.

The regular expression attribute is very useful since you can describe exactly what format you want a string property to be in. While using this though I ran into a problem. The attribute doesn’t let you specify RegexOptions. This was an issue for me since I wanted to use the regex to validate that the users input was between 5 and 200 characters long , so I had attribute that property as such:

        1: [RegularExpression(@".{5,200}")]

       2: public string Text{get;set;}

However this doesn’t work since by default the wildcard . does not match new lines (which I am allowing in the input). The way to fix this is to specify the RegexOptions.SingleLine option to either the Regex constructor or Match function. The problem is I have no way of doing that here, and there is no argument on the attribute constructor to specify those options. I was considering overriding the attribute to create one that allows specifying the attribute but then I stumbled upon this:

Regular Expression Options

You are able to specify the regex option inside of the regular expression text! (which I thought was a huge discovery until my co-worker said he knew this all along but never let me know!).

So I just changed the expression to look like this:

       1: [RegularExpression(@"(?s).{5,200}")]

       2: public string Text{get; set;}

The (?s) is the inline regex option definition so say I want this in SingleLine mode! And now the validation works the way I wanted!

Model Binder

MattManela — Tue, 16 Dec 2008 06:45:27 GMT

When working with a multi-tier application I often find myself converting from one of the tiers object models to my own similar (but often different) model. I often write code that would set one by one each property from a web tier object to my object. In order to make this easier I wrote this object binder. It is a fake deep copy in a way. You tell it what destination type you want to build and give it a source object and it will go through each property (matching by names) and checks if it can copy from that property from the source to the destination. If it can’t it will call itself again on that object to try to copy its properties.

Here is the code:

        1: using System;

       2: using System.Reflection;

       3: using System.Collections;

       4:  

       5: namespace Binder

       6: {

       7:     public class ObjectBinder

       8:     {

       9:         /// <summary>

        /// Copies one object to an instance of a different type.

        /// 

        /// Assumptions:

        /// Object which implements IList'1 also implements IList 

        /// Object which implements IDictionary'2 also implements IDictionary 

        /// </summary>

        /// <typeparam name="T"></typeparam>

        /// <param name="source">The source.</param>

        /// <returns></returns>

        public static T Copy<T>(object source) where T : new()

        {

            return (T)Copy(source, typeof(T));

        }

  

  

        private static object Copy(object source, Type destinationType)

        {

            if (source == null) throw new ArgumentNullException("source", "source must not be null");

  

            var destination = Activator.CreateInstance(destinationType);

  

            var sourceProperties = source.GetType().GetProperties();

            foreach (var sourceProp in sourceProperties)

            {

                var sourcePropType = sourceProp.PropertyType;

                var destinationProp = destination.GetType().GetProperty(sourceProp.Name);

  

                if (sourceProp.CanRead && destinationProp != null && destinationProp.CanWrite)

                {

                    var destinationPropType = destinationProp.PropertyType;

                    Type sourcePropInterfaceType = null;

                    Type destinationPropInterfaceType = null;

  

                    // Skip indexer properties

                    if (sourceProp.GetIndexParameters().Length > 0) continue;

                    

                    var sourceValue = sourceProp.GetValue(source, null);

                    if (sourceValue == null) continue;

  

                    object destinationValue = null;

                    if (destinationPropType.IsAssignableFrom(sourcePropType))

                    {

                        destinationValue = sourceValue;

                    }

                    else if (

                        (sourcePropInterfaceType = sourcePropType.GetInterface("IList`1", true)) != null &&

                        (destinationPropInterfaceType = destinationPropType.GetInterface("IList`1", true)) != null)

                    {

  

                        var sourceArgType = sourcePropInterfaceType.GetGenericArguments()[0];

                        var destArgType = destinationPropInterfaceType.GetGenericArguments()[0];

                        bool isAssignable = destArgType.IsAssignableFrom(sourceArgType);

  

                        IList listCopy = null;

  

                        if (destinationPropType.IsArray)

                        {

                            // If array there must be a one argument constructor

                            listCopy = (IList)Activator.CreateInstance(destinationPropType, ((IList)sourceValue).Count);

                        }

                        else

                        {

                            // If not an array require a parameterless constructor

                            if (destinationPropType.GetConstructor(Type.EmptyTypes) == null) continue;

                            listCopy = (IList)Activator.CreateInstance(destinationPropType);

                        }

  

                        int index = 0;

                        foreach (var item in ((IList)sourceValue))

                        {

                            var itemCopy = item;

                            if (!isAssignable)

                                itemCopy = Copy(item, destArgType);

  

                            if (destinationPropType.IsArray)

                                listCopy[index] = itemCopy;

                            else

                                listCopy.Add(itemCopy);

  

                            index++;

                        }

  

                        destinationValue = listCopy;

                    }

                    else if (

                        (sourcePropInterfaceType = sourcePropType.GetInterface("IDictionary`2", true)) != null &&

                        (destinationPropInterfaceType = destinationPropType.GetInterface("IDictionary`2", true)) != null)

                    {

  

                        var sourceArgTypes = sourcePropInterfaceType.GetGenericArguments();

                        var destArgTypes = destinationPropInterfaceType.GetGenericArguments();

                        bool isKeyAssignable = destArgTypes[0].IsAssignableFrom(sourceArgTypes[0]);

                        bool isValueAssignable = destArgTypes[1].IsAssignableFrom(sourceArgTypes[1]);

  

                        var defaultConstructor = destinationPropType.GetConstructor(Type.EmptyTypes);

                        if (defaultConstructor == null) continue;

                        var dictionaryCopy = Activator.CreateInstance(destinationPropType) as IDictionary;

  

                        foreach (DictionaryEntry pair in ((IDictionary)sourceValue))

                        {

                            var keyCopy = pair.Key;

                            var valueCopy = pair.Value;

                            if (!isKeyAssignable)

                                keyCopy = Copy(keyCopy, destArgTypes[0]);

                            if (!isValueAssignable)

                                valueCopy = Copy(valueCopy, destArgTypes[1]);

  

                            dictionaryCopy.Add(keyCopy, valueCopy);

                        }

  

                        destinationValue = dictionaryCopy;

                    }

                    else

                    {

                        destinationValue = Copy(sourceValue, destinationPropType);

                    }

  

  

                    destinationProp.SetValue(destination, destinationValue, null);

  

                }

            }

  

  

            return destination;

        }

    }

}

And the tests using XUnit.Net:

       1: using System;

       2: using System.Collections.Generic;

       3: using System.Linq;

       4: using System.Text;

       5: using Xunit;

       6: using System.Collections.ObjectModel;

       7:  

       8: namespace Binder

       9: {

    public class ObjectBinderFacts

    {

        public class The_Copy_Method

        {

  

            [Fact]

            public void throws_if_source_is_null()

            {

  

                Exception ex = Record.Exception(() => ObjectBinder.Copy<Destination>(null));

  

                Assert.IsType<ArgumentNullException>(ex);

                Assert.Equal("source", ((ArgumentNullException)ex).ParamName);

            }

  

            [Fact]

            public void will_copy_assignable_scalar_property()

            {

                var source = new Source();

  

                var res = ObjectBinder.Copy<Destination>(source);

  

                Assert.Equal(source.A, res.A);

                Assert.Equal(source.B, res.B);

                Assert.Equal(source.C, res.C);

                Assert.Equal(source.D, res.D);

                Assert.Equal(source.E, res.E);

  

            }

  

            [Fact]

            public void will_copy_assignable_generic_list_property()

            {

                var source = new Source();

  

                var res = ObjectBinder.Copy<Destination>(source);

  

                Assert.Equal(source.F.Count, res.F.Count);

                Assert.Equal(source.F[0], res.F[0]);

                Assert.Equal(source.F[1], res.F[1]);

  

            }

  

            [Fact]

            public void will_copy_assignable_array_property()

            {

                var source = new Source();

  

                var res = ObjectBinder.Copy<Destination>(source);

  

                Assert.Equal(source.N.Length, res.N.Length);

                Assert.Equal(source.N[0], res.N[0]);

                Assert.Equal(source.N[1], res.N[1]);

  

            }

  

            [Fact]

            public void will_copy_unassignable_array_property()

            {

                var source = new Source();

  

                var res = ObjectBinder.Copy<Destination>(source);

  

                Assert.Equal(source.O.Length, res.O.Length);

                Assert.Equal(source.O[0].Value, res.O[0].Value);

                Assert.Equal(source.O[1].Value, res.O[1].Value);

  

            }

  

            [Fact]

            public void will_copy_assignable_generic_dictionary_property()

            {

                var source = new Source();

  

                var res = ObjectBinder.Copy<Destination>(source);

  

                Assert.Equal(source.J.Count, res.J.Count);

                Assert.Equal(source.J["a"], res.J["a"]);

                Assert.Equal(source.J["b"], res.J["b"]);

  

            }

  

            [Fact]

            public void will_copy_unassignable_generic_dictionary_with_assignable_keys_and_values()

            {

                var source = new Source();

  

                var res = ObjectBinder.Copy<Destination>(source);

  

                Assert.Equal(source.K.Count, res.K.Count);

                Assert.Equal(source.K["a"], res.K["a"]);

                Assert.Equal(source.K["b"], res.K["b"]);

  

            }

  

            [Fact]

            public void will_copy_unassignable_generic_dictionary_with_assignable_keys_and_unassignable_values()

            {

                var source = new Source();

  

                var res = ObjectBinder.Copy<Destination>(source);

  

                Assert.Equal(source.L.Count, res.L.Count);

                Assert.Equal(source.L["a"].Value, res.L["a"].Value);

                Assert.Equal(source.L["b"].Value, res.L["b"].Value);

  

            }

  

            [Fact]

            public void will_copy_unassignable_generic_dictionary_with_unassignable_keys_and_unassignable_values()

            {

                var source = new Source();

  

                var res = ObjectBinder.Copy<Destination>(source);

  

                Assert.Equal(source.M.Count, res.M.Count);

                Assert.Equal(source.M[new SomeObject { Value = 1 }].Value, res.M[new OtherObject { Value = 1 }].Value);

                Assert.Equal(source.M[new SomeObject { Value = 2 }].Value, res.M[new OtherObject { Value = 2 }].Value);

  

            }

  

            [Fact]

            public void will_copy_unassignable_generic_list_with_assignable_values()

            {

                var source = new Source();

  

                var res = ObjectBinder.Copy<Destination>(source);

  

                Assert.Equal(source.G.Count, res.G.Count);

                Assert.Equal(source.G[0], res.G[0]);

                Assert.Equal(source.G[1], res.G[1]);

  

            }

  

            [Fact]

            public void will_copy_unassignable_object_property()

            {

                var source = new Source();

  

                var res = ObjectBinder.Copy<Destination>(source);

  

                Assert.Equal(source.H.Value, res.H.Value);

  

            }

  

            [Fact]

            public void will_copy_unassignable_generic_list_properties()

            {

                var source = new Source();

  

                var res = ObjectBinder.Copy<Destination>(source);

  

                Assert.Equal(source.I.Count, res.I.Count);

                Assert.Equal(source.I[0].Value, res.I[0].Value);

                Assert.Equal(source.I[1].Value, res.I[1].Value);

  

            }

  

            [Fact]

            public void will_return_object_with_default_values_if_no_properties_match()

            {

                var source = new Source();

  

                var res = ObjectBinder.Copy<SomeObject>(source);

  

                Assert.Equal(0, res.Value);

            }

  

            class SomeObject

            {

                public int Value { get; set; }

  

                public override int GetHashCode()

                {

                    return Value;

                }

  

                public override bool Equals(object obj)

                {

                    var some = obj as SomeObject;

                    if (obj == null) return false;

                    return some.Value == Value;

                }

            }

  

            class OtherObject

            {

                public int Value { get; set; }

  

                public override int GetHashCode()

                {

                    return Value;

                }

  

                public override bool Equals(object obj)

                {

                    var some = obj as OtherObject;

                    if (obj == null) return false;

                    return some.Value == Value;

                }

            }

  

            class OtherDictionary<TKey, TValue> : Dictionary<TKey, TValue>

            {

  

            }

  

            class Source

            {

                public Source()

                {

                    A = "String";

                    B = 5;

                    C = Guid.NewGuid();

                    D = 5.5;

                    E = 'a';

                    F = new List<int> { 1, 2 };

                    G = new List<string> { "a", "b" };

                    H = new SomeObject();

                    I = new List<SomeObject> { new SomeObject { Value = 1 }, new SomeObject { Value = 2 } };

                    J = new Dictionary<string, int> { { "a", 1 }, { "b", 2 } };

                    K = new Dictionary<string, int> { { "a", 1 }, { "b", 2 } };

                    L = new Dictionary<string, SomeObject> { { "a", new SomeObject { Value = 1 } }, { "b", new SomeObject { Value = 2 } } };

                    M = new Dictionary<SomeObject, SomeObject> {

                        { new SomeObject { Value = 1 }, new SomeObject { Value = 10 } }, 

                        { new SomeObject { Value = 2 }, new SomeObject { Value = 20 } } 

                    };

                    N = new[] { 1, 2 };

                    O = new[] { new SomeObject { Value = 1 }, new SomeObject { Value = 2 } };

                }

  

                // Assignable

                public string A { get; set; }

                public int B { get; set; }

                public Guid C { get; set; }

                public double D { get; set; }

                public char E { get; set; }

                public List<int> F { get; set; }

                public Dictionary<string, int> J { get; set; }

                public int[] N { get; set; }

  

                // Not assignable

                public List<string> G { get; set; }

                public SomeObject H { get; set; }

                public List<SomeObject> I { get; set; }

                public Dictionary<string, int> K { get; set; }

                public Dictionary<string, SomeObject> L { get; set; }

                public Dictionary<SomeObject, SomeObject> M { get; set; }

                public SomeObject[] O { get; set; }

            }

  

  

            class Destination

            {

                public string A { get; set; }

                public int B { get; set; }

                public Guid C { get; set; }

                public double D { get; set; }

                public char E { get; set; }

                public List<int> F { get; set; }

                public Dictionary<string, int> J { get; set; }

                public int[] N { get; set; }

  

                public Collection<string> G { get; set; }

                public OtherObject H { get; set; }

                public List<OtherObject> I { get; set; }

                public OtherDictionary<string, int> K { get; set; }

                public Dictionary<string, OtherObject> L { get; set; }

                public Dictionary<OtherObject, OtherObject> M { get; set; }

                public OtherObject[] O { get; set; }

            }

        }

    }

}

One possible enhancement I thought about was to add a attribute to indicate on the destination model that is maps to a property of a different name. I haven’t had a need for it yet but I will surely add it when I do.

Updated JQuery ResizeComplete method

MattManela — Tue, 02 Dec 2008 14:51:29 GMT

I made 2 slight changes and I think it works pretty well now. I now detect if the browser is Firefox and use the regular resize event since its resize behaves like a resizeComplete. I also modified the timeout a bit since I think 100 ms might be too small.

Here is the updated version:

   1: jQuery.fn.resizeComplete = function(callback)   2: {   3:     4:   var element = this;   5:   var height = element.height();   6:   var width = element.width();   7:   var monitoring = false;   8:   var timer;   9:     10:   function monitorResizing()  11:   {  12:     monitoring = true;  13:       14:     var newHeight = element.height();  15:     var newWidth = element.width();  16:       17:     if(newHeight != height || newWidth != width)  18:     {  19:       height = newHeight;  20:       width = newWidth;  21:       timer = setTimeout(function() { monitorResizing() },200);  22:     }  23:     else  24:     {  25:       monitoring = false;  26:       clearTimeout(timer);  27:       callback();  28:     }  29:   }  30:     31:   function onResize()  32:   {  33:     if(monitoring) return;  34:     monitorResizing();  35:   }  36:     37:   if($.browser.mozilla)  38:   {  39:     element.resize(callback);  40:   }  41:   else  42:   {  43:     element.resize(onResize);  44:   }  45:     46:     47: }

Rough draft of a new JQuery method

MattManela — Tue, 25 Nov 2008 04:41:17 GMT

I have run into issues recently with the browsers' implementation of the resize event on the window. Opera, Safari, IE and Firefox all have different behaviors when this event is fired.

Firefox only fires it when you release the mouse.
IE fires this event many many times while resizing.
Safari will fire continusouly while dragging
Opera fires after the resizing stopped

You can read more about this here.

These differences led me to search for a solution. I quickly wrote this proof of concept function today which may help solve this problem. It is a JQuery add-on called resizeComplete. It works by checking periodically after a resize starts and checks if the size of the object has changed. Once no change is detected it invokes the call back method.

This has not been tested much at all but I think it might be on the right track.

   1: jQuery.fn.resizeComplete = function(callback)   2: {   3:     4:   var element = this;   5:   var height = element.height();   6:   var width = element.width();   7:   var monitoring = false;   8:   var timer;   9:     10:   function monitorResizing()  11:   {  12:     monitoring = true;  13:       14:     var newHeight = element.height();  15:     var newWidth = element.width();  16:       17:     if(newHeight != height || newWidth != width)  18:     {  19:       height = newHeight;  20:       width = newWidth;  21:       timer = setTimeout(function() { monitorResizing() },100);  22:     }  23:     else  24:     {  25:       monitoring = false;  26:       clearTimeout(timer);  27:       callback();  28:     }  29:   }  30:     31:   function onResize()  32:   {  33:     if(monitoring) return;  34:     monitorResizing();  35:   }  36:     37:   element.resize(onResize);  38:     39: }

Here is an example of its usage:

   1: $(document).ready(function()   2: {   3:   $(window).resizeComplete(function(){ document.write('hi') });   4: }   5: );

Parameterized State Transformer Monad in F#?

MattManela — Wed, 05 Nov 2008 05:30:29 GMT

I have have been playing around with F# and I decided to create a state monad. This worked out really well since I was able to leverage the F# computation expressions. I then decided to try to extend this and make it more general by creating a parameterized state transformer monad. This is a state monad which encapsulates another monad. What this allow you to do is turn any computation into a statefull one.

This concept exists in Haskell which you can see here. However, my attempts at replicating this in F# failed. Unlike in Haskell, the computation expressions in F# don't share a common interface (or type class). This prevents a computation from being able to generically take another computation as a parameter. The reason is that an operation on the parameterized state transformer monad such as bind will result in a bind called on its encapsulated monad. But since there is no interface for computations there is no bind method to call.

I attempted to fix this by creating my own monad interface but this didn't work:

   1: type Monad =   2:     abstract Bind : 'm * ('a -> 'm) -> 'm   3:     abstract Delay : (unit ->'m) -> 'm   4:     abstract Let : 'a * ('a -> 'm) -> 'm   5:     abstract Return : 'a -> 'm   6:     abstract Zero : unit -> 'm   7:     abstract Combine : 'm -> 'm2 -> 'm3   8:     abstract Run : (unit ->'m) -> 'm

After playing with that and failing I ended up with a less than ideal solution. Given a Maybe monad like below:

   1: // Maybe Monad       2: type MaybeBuilder() =   3:     member b.Return(x) = Some x   4:     member b.Run(f) = f()   5:     member b.Delay(f) = f   6:     member b.Let(p,rest) = rest p   7:     member b.Zero () = None   8:     member b.Combine(m1,dm2) = match m1 with   9:                                  | None -> dm2()  10:                                  | x -> x  11:    12:     member b.Bind(p,rest) = match p with   13:                             | None -> None  14:                             | Some r -> rest r

I created a state transformer monad which take an argument of type m:MaybeBuilder

   1: type StateMBuilder(m:MaybeBuilder) =    2:     member b.Return(x) = fun s -> m.Return (x,s)   3:     member b.Run(f) = fun inp -> (f inp)()   4:     member b.Delay(f) = fun inp -> fun () -> f() inp   5:     member b.Let(p,rest) = rest p   6:     member b.Zero () = fun s -> m.Zero()   7:     member b.Bind(p,rest) = fun s -> m.Bind(p s,fun (v,s2) -> rest v s2)   8:     member b.Combine(p1,dp2) = fun s -> m.Combine(p1 s, dp2 s)   9:    10:     // State specific functions  11:     member b.Update f = fun s -> try m.Return (s, f s) with e -> m.Zero()  12:     member b.Read () = b.Update id  13:     member b.Set t = b.Update (fun _ -> t)

Now although this type is technically parameterized ;) it isn't really the idea since its not generic, it has to be a MaybeBuilder. To use this with a different monad I would need to change m:MaybeBuild to m:SomeOtherMonad.

I am still going to play with this but this is as far as I have gotten.

After all of that here is how you create a state transformer monad parameterized over the maybe monad:

   1: let maybe = MaybeBuilder()   2: let state = StateMBuilder(maybe)

If anyone has an idea how I can make this work I would love to hear it.

What annoys me when writing generic functions in Visual Studio...

MattManela — Tue, 14 Oct 2008 17:38:18 GMT

When writing a generic function I start from left to right (the same way I write most things except when I took Yiddish in college). For example, Lets say I am writing a simple generic method which return the first element of a generic list. I want the signature of this method to be:

private T First<T>(List<T> list)

I start by writing the visibility:

private

I then need to write the return type so I type T. The problem is that since T is not defined as a generic type parameter yet so intellisense tries to help me out by showing me all types that begin with T:

Now my instinct here (every time) is to press space since I just want to move on to the next word since T is all I want. But space will auto-complete T with ThreadStaticAtrribute. What I need to do is press esc to close the intellisense window and then press space. This may seems like a silly issue, but I seem to never remember that I need to do this.

Visual Studio and intellisense have done nothing wrong here , I just wish intellisense had the ability to read my mind and understand exactly what I am intended to do. It could save me a couple key presses a day!

SQL CE 3.5 with LINQ to SQL Revisited

MattManela — Fri, 26 Sep 2008 15:26:08 GMT

A few days ago I made a post about using SQL CE 3.5 with LINQ to SQL. I described a way to use connection pooling with SQL CE. A gracious blog reader (Mike Brown) pointed out a way I could make my solution much simpler by using the [ThreadStatic] attribute. I never heard of this attribute but it is really nifty. You mark a field with it and then each thread that accesses that field will be accessing a unique instance of it!

Using this attribute my code for connection pooling went from this:

/// <summary>
/// Manages open connections on a per-thread basis
/// </summary>
public class ConnectionPool
{
    private Dictionary<int, IDbConnection> threadConnectionMap;
 
    /// <summary>
    /// Gets the connection string.
    /// </summary>
    /// <value>The connection string.</value>
    public string ConnectionString
    {
        get;
        private set;
    }
 
    /// <summary>
    /// Gets a connection.
    /// </summary>
    /// <returns>An open connection</returns>
    public IDbConnection Connection
    {
        get
        {
            lock (threadConnectionMap)
            {
                int threadId = Threading.Thread.CurrentThread.ManagedThreadId;
 
                IDbConnection connection = null;
                if (threadConnectionMap.ContainsKey(threadId))
                {
                    connection = threadConnectionMap[threadId];
                }
                else
                {
                    connection = new SqlCeConnection(ConnectionString);
                    connection.Open();
                    threadConnectionMap.Add(threadId, connection);
                }
 
                return connection;
            }
        }
    }
 
    /// <summary>
    /// Initializes a new instance of the <see cref="ConnectionPool"/> class.
    /// </summary>
    /// <param name="connectionString">The connection string.</param>
    public ConnectionPool(string connectionString)
    {
        threadConnectionMap = new Dictionary<int, IDbConnection>();
        ConnectionString = connectionString;
    }

to this:

/// <summary>
    /// Manages open connections on a per-thread basis
    /// </summary>
    public class ConnectionPool
    {
        [ThreadStatic]
        private IDbConnection threadConnection;

        /// <summary>
        /// Gets the connection string.
        /// </summary>
        /// <value>The connection string.</value>
        public string ConnectionString
        {
            get;
            private set;
        }

        /// <summary>
        /// Gets a connection.
        /// </summary>
        /// <returns>An open connection</returns>
        public IDbConnection Connection
        {
            get
            {
                if (threadConnection == null)
                {
                    threadConnection = new SqlCeConnection(ConnectionString);
                    threadConnection.Open();
                }

                return threadConnection;
            }
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="ConnectionPool"/> class.
        /// </summary>
        /// <param name="connectionString">The connection string.</param>
        public ConnectionPool(string connectionString)
        {
            ConnectionString = connectionString;
        }
    }

Very nice and clean.

Thanks Mike!