C# 4 and .NET 4

egular expressions ❘ 217
That is all you have to do! Notice how you take the precaution of checking whether format is null before
you call any methods against this parameter — you want this method to be as robust as reasonably possible.
The format specifiers for all the primitive types are case-insensitive, so that is the behavior that other
developers are going to expect from your class, too. For the format specifier VE, you need each component to
be formatted in scientific notation, so you just use String.Format() again to achieve this. The fields x, y,
and z are all doubles. For the case of the IJK format specifier, there are quite a few substrings to be added
to the string, so you use a StringBuilder object to improve performance.
For completeness, you also reproduce the no-parameter ToString() overload developed earlier:
public override string ToString()
{
return "( " + x + ", " + y + ", " + z + " )";
}
Finally, you need to add a Norm() method that computes the square (norm) of the vector because you didn’t
actually supply this method when you developed the Vector struct:
public double Norm()
{
return x*x + y*y + z*z;
}
Now you can try your formattable vector with some suitable test code:
static void Main()
{
Vector v1 = new Vector(1,32,5);
Vector v2 = new Vector(845.4, 54.3, -7.8);
Console.WriteLine("\nIn IJK format,\nv1 is {0,30:IJK}\nv2 is {1,30:IJK}",
v1, v2);
Console.WriteLine("\nIn default format,\nv1 is {0,30}\nv2 is {1,30}", v1, v2);
Console.WriteLine("\nIn VE format\nv1 is {0,30:VE}\nv2 is {1,30:VE}", v1, v2);
Console.WriteLine("\nNorms are:\nv1 is {0,20:N}\nv2 is {1,20:N}", v1, v2);
}
The result of running this sample is this:
FormattableVector
In IJK format,
v1 is 1 i + 32 j + 5 k
v2 is 845.4 i + 54.3 j + -7.8 k
In default format,
v1 is ( 1, 32, 5 )
v2 is ( 845.4, 54.3, -7.8 )
In VE format
v1 is ( 1.000000E+000, 3.200000E+001, 5.000000E+000 )
v2 is ( 8.454000E+002, 5.430000E+001, -7.800000E+000 )
Norms are:
v1 is || 1050 ||
v2 is || 717710.49 ||
This shows that your custom specifiers are being picked up correctly.
regular eXPressions
Regular expressions are part of those small technology areas that are incredibly useful in a wide range of
programs, yet rarely used among developers. You can think of regular expressions as a mini-programming
language with one specific purpose: to locate substrings within a large string expression. It is not a new
technology; it originated in the UNIX environment and is commonly used with the Perl programming language.
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