SirMike's Techblog

Creating enum which sucks

April 22nd, 2009

We create many enumerations in our programs. But sometimes we can make a mistake that drives somebody else mad.

Let's suppose that the first programmer created an enum like this:

PLAIN TEXT

C#:

enum Mood
{
Unknown = -1,
Awesome,
Cool,
Bad,
Awful
}

It does not look bad at the first look, yet another enum.

Another programmer created a list:

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C#:

List<mood> availableMoods = new List<mood>();
availableMoods.Add(Mood.Awful);
availableMoods.Add(Mood.Bad);

Then he would like to find there a first mood type which is a part of "good mood" group and pass the result to another layer of an application. He wrote the code:

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C#:

Mood found = availableMoods.Find(
delegate(Mood f)
{
return f == Mood.Awesome || f == Mood.Cool;
}
);

Now he realized that it cannot work because Find method of a List(T) class returns default(T) when a list does not contain desired item. In this case he would get Mood.Awesome because it is the default value of the enum. I do not need to add that the Mood.Awesome is not even the part of the list.

We can solve this problem by several different approaches.

Create different enum where the default element will be "Unknown = 0"
Use FindIndex method of List(T) class so we will be able to handle the situation of not found element
I believe that other approaches could work as well

The question to discuss - which programmer made a mistake? The first one who created "unfortunate" enum or the second one who used wrong structure / wrong searching method?

Posted in .NET Framework, C#, Programming | 1 Comment »

Unit testing and objects equality

February 16th, 2009

Let's assume that we have a class like below:

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C#:

public class Foo : IEquatable<Foo>
{
private int variable;
public int Variable
{
get { return variable; }
set { variable = value; }
}
#region IEquatable<Foo> Members
public bool Equals(Foo other)
{
return this.variable == other.Variable;
}
#endregion
}

and a unit test for that:

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C#:

[TestClass()]
public class FooTest
{
[TestMethod()]
public void EqualsTest()
{
Foo one = new Foo();
one.Variable = 5;
Foo two = new Foo();
two.Variable = 5;
Assert.AreEqual<Foo>(one, two, "AreEqual<Foo> failed");
Assert.AreEqual(one, two, "AreEqual failed");
Assert.AreSame(one, two, "AreSame failed");
}
}

and a question is - which Assert fails? All of them o_O
I could not find an explanation why implemented Equals method is not called. Framework always calls default Equals(object)