Topics covered:
- The Concept of Self-Documenting Code
- Bad Comments
- Good Programming Style
- To Comment or not to Comment?
- Key Points commenting
- Recommended Practices
- C# XML Documentation Comments
Video (in Bulgarian)
Presentation Content
What is Project Documentation?
- Consists of documents and information
- Both inside the source-code and outside
- External documentation
- At a higher level compared to the code
- Problem definition, requirements, architecture, design, project plans, test plans. etc.
- Internal documentation
- Lower-level – explains a class,method or a piece of code
Programming Style
- Main contributor to code-level documentation
- The program structure
- Straight-forward, easy-to-read and easily understandable code
- Good naming approach
- Clear layout and formatting
- Clear abstractions
- Minimized complexity
- Loose coupling and strong cohesion
Bad Comments – Example
public static List<int> FindPrimes(int start, int end)
{
// Create new list of integers
List<int> primesList = new List<int>();
// Perform a loop from start to end
for (int num = start; num <= end; num++)
{
// Declare boolean variable, initially true
bool prime = true;
// Perform loop from 2 to sqrt(num)
for (int div = 2; div <= Math.Sqrt(num); div++)
{
// Check if div divides num with no remainder
if (num % div == 0)
{
// We found a divider -> the number is not prime
prime = false;
// Exit from the loop
break;
}
// Continue with the next loop value
}
// Check if the number is prime
if (prime)
{
// Add the number to the list of primes
primesList.Add(num);
}
}
// Return the list of primes
return primesList;
}
Self-Documenting Code – Example
public static List<int> FindPrimes(int start, int end)
{
List<int> primesList = new List<int>();
for (int num = start; num <= end; num++)
{
bool isPrime = IsPrime(num);
if (isPrime)
{
primesList.Add(num);
}
}
return primesList;
}
Good code does not need comments. It is self-explaining.
private static bool IsPrime(int num)
{
bool isPrime = true;
int maxDivider = Math.Sqrt(num);
for (int div = 2; div <= maxDivider; div++)
{
if (num % div == 0)
{
// We found a divider -> the number is not prime
isPrime = false;
break;
}
}
return isPrime;
}
Good methods have good name and are easy to read and understand.
This comment explain non-obvious details. It does not repeat the code.
Bad Programming Style – Example
for (i = 1; i <= num; i++)
{
meetsCriteria[i] = true;
}
for (i = 2; i <= num / 2; i++)
{
j = i + i;
while (j <= num)
{
meetsCriteria[j] = false;
j = j + i;
}
}
for (i = 1; i <= num; i++)
{
if (meetsCriteria[i])
{
Console.WriteLine(i + " meets criteria.");
}
}
Uninformative variable names. Crude layout.
Good Programming Style – Example
for (primeCandidate = 1; primeCandidate <= num; primeCandidate++)
{
isPrime[primeCandidate] = true;
}
for (int factor = 2; factor < (num / 2); factor++)
{
int factorableNumber = factor + factor;
while (factorableNumber <= num)
{
isPrime[factorableNumber] = false;
factorableNumber = factorableNumber + factor;
}
}
for (primeCandidate = 1; primeCandidate <= num; primeCandidate++)
{
if (isPrime[primeCandidate])
{
Console.WriteLine(primeCandidate + " is prime.");
}
}
Self-Documenting Code
- Code that relies on good programming style
- To carry major part of the information intended for the documentation
- Self-documenting code fundamental principles
The best documentation is the code itself.
Make the code self-explainable and self-documenting, easy to read and understand.
Do not document bad code, rewrite it!
Self-Documenting Code Checklist
- Classes
- Does the class’s interface present a consistent abstraction?
- Does the class’s interface make obvious how you should use the class?
- Is the class well named, and does its name describe its purpose?
- Can you treat the class as a black box?
- Do you reuse instead of repeating code?
- Methods
- Does each routine’s name describe exactly what the method does?
- Does each method perform one well-defined task with minimal dependencies?
- Data Names
- Are type names descriptive enough to help document data declarations?
- Are variables used only for the purpose for which they’re named?
- Data Names
- Does naming conventions distinguish among type names, enumerated types, named constants, local variables, class variables, and global variables?
- Others
- Are data types simple so that they minimize complexity?
- Are related statements grouped together?
Effective Comments
- Effective comments do not repeat the code
- They explain it at a higher level and reveal non-obvious details
- The best software documentation is the source code itself – keep it clean and readable!
- Self-documenting code is self-explainable and does not need comments
- Simple design, small well named methods, strong cohesion and loose coupling, simple logic, good variable names, good formatting, …
Effective Comments – Mistakes
- Misleading comments
// write out the sums 1..n for all n from 1 to num
current = 1;
previous = 0;
sum = 1;
for (int i = 0; i < num; i++)
{
Console.WriteLine( "Sum = " + sum );
sum = current + previous;
previous = current;
current = sum;
}
What problem does this algorithm solve?
Can you guess that sum is equal to the ith Fibonacci number?
- Comments repeating the code:
// set product to "base"
product = base;
// loop from 2 to "num"
for ( int i = 2; i <= num; i++ )
{
// multiply "base" by "product"
product = product * base;
}
Console.WriteLine( "Product = " + product );
- Poor coding style:
// compute the square root of Num using
// the Newton-Raphson approximation
r = num / 2;
while (abs(r - (num/r)) > TOLERANCE)
{
r = 0.5 * (r + (num/r) );
}
Console.WriteLine( "r = " + r );
- Do not comment bad code, rewrite it
Key Points for Effective Comments
- Use commenting styles that don’t break down or discourage modification
// Variable Meaning
// -------- -------
// xPos .............. X coordinate position (in meters)
// yPos .............. Y coordinate position (in meters)
// zPos .............. Z coordinate position (in meters)
// radius ............ The radius of the sphere where the
battle ship is located (in meters)
// distance .......... The distance from the start position
(in meters)
- The above comments are unmaintainable
- Comment the code intent, not implementation details
// Scan char by char to find the command-word terminator ($)
done = false;
maxLen = inputString.Length;
i = 0;
while (!done && (i < maxLen))
{
if (inputString[i] == '$')
{
done = true;
}
else
{
i++;
}
}
- Focus your documentation efforts on the code
// Find the command-word terminator
foundTheTerminator = false;
maxCommandLength = inputString.Length();
testCharPosition = 0;
while (!foundTheTerminator &&
(testCharPosition < maxCommandLength))
{
if (inputString[testCharPosition] == COMMAND_WORD_TERMINATOR)
{
foundTheTerminator = true;
terminatorPosition = testCharPosition;
}
else
{
testCharPosition = testCharPosition + 1;
}
}
Better code → less comments
- Focus paragraph comments on the why rather than the how
// Establish a new account
if (accountType == AccountType.NewAccount)
{
…
}
- Use comments to prepare the reader for what is to follow
- Avoid abbreviations
- Comment anything that gets around an error or an undocumented feature
- E.g. // This is workaround for bug #3712
- Justify violations of good programming style
- Don’t comment tricky code – rewrite it
- Use built-in features for commenting
- XML comments in C#
- JavaDoc in Java, …
General Guidelines for Higher Level Documentation
- Describe the design approach to the class
- Describe limitations, usage assumptions, and so on
- Comment the class interface (public methods / properties / events / constructors)
- Don’t document implementation details in the class interface
- Describe the purpose and contents of each file
- Give the file a name related to its contents
C# XML Documentation
- In C# you can document the code by XML tags in special comments
- Directly in the source code
- For example:
/// <summary>
/// This class performs an important function.
/// </summary>
public class MyClass { }
- The XML doc comments are not metadata
- Not included in the compiled assembly and not accessible through reflection
XML Documentation Tags
- <summary>
- A summary of the class / method / object
- <param>
<param name="name">description</param>- Describes one of the parameters for a method
- <returns>
- A description of the returned value
- <remarks>
- Additional information (remarks)
- <c> and <code>
- Gives you a way to indicate code
- <see> and <seealso> and cref
- Code reference
<seealso cref="TestClass.Main"/>
- Code reference
- <exception>
<exception cref="type">description</exception>- Lets you specify which exceptions can be thrown
- All tags: http://msdn.microsoft.com/en-us/library/5ast78ax.aspx
XML Documentation Example
/// <summary>
/// The GetZero method. Always returns zero.
/// </summary>
/// <example>
/// This sample shows how to call the <see cref="GetZero"/> method.
/// <code>
/// class TestClass
/// {
/// static int Main()
/// {
/// return GetZero();
/// }
/// }
/// </code>
/// </example>
public static int GetZero()
{
return 0;
}
C# XML Documentation
- Visual Studio will use the XML documentation for autocomplete
- Automatically, just use XML docs
- Compiling the XML documentation:
- Compile with /doc the to extract the XML doc into an external XML file
- Use Sandcastle or other tool to generate CHM / PDF / HTML / other MSDN-style documentation
- Example: http://www.ewoodruff.us/shfbdocs/