#Maintainability Guidelines
A method that requires more than 7 statements is simply doing too much or has too many responsibilities. It also requires the human mind to analyze the exact statements to understand what the code is doing. Break it down into multiple small and focused methods with self-explaining names, but make sure the high-level algorithm is still clear.
To make a more conscious decision on which members to make available to other classes, first restrict the scope as much as possible. Then carefully decide what to expose as a public member or type.
Although a property like customer.HasNoOrders makes sense, avoid using it in a negative condition like this:
bool hasOrders = !customer.HasNoOrders;
Double negatives are more difficult to grasp than simple expressions, and people tend to read over the double negative easily.
All DLLs should be named according to the pattern Company.Component.dll where Company refers to your company's name and Component contains one or more dot-separated clauses. For example AvivaSolutions.Web.Controls.dll.
As an example, consider a group of classes organized under the namespace AvivaSolutions.Web.Binding exposed by a certain assembly. According to this guideline, that assembly should be called AvivaSolutions.Web.Binding.dll.
Exception: If you decide to combine classes from multiple unrelated namespaces into one assembly, consider suffixing the assembly name with Core, but do not use that suffix in the namespaces. For instance, AvivaSolutions.Consulting.Core.dll.
Use Pascal casing to name the file and don't use underscores.
Exception: Nested types should, for obvious reasons, be part of the same file.
When using partial types and allocating a part per file, name each file after the logical part that part plays. For example:
// In MyClass.cs
public partial class MyClass
{...}
// In MyClass.Designer.cs
public partial class MyClass
{...}
Limit usage of fully qualified type names to prevent name clashing. For example, don't do this:
var list = new System.Collections.Generic.List();
Instead, do this:
using System.Collections.Generic;
var list = new List();
If you do need to prevent name clashing, use a using directive to assign an alias:
using Label = System.Web.UI.WebControls.Label;
Don't use literal values, either numeric or strings, in your code, other than to define symbolic constants. For example:
public class Whatever
{
public static readonly Color PapayaWhip = new Color(0xFFEFD5);
public const int MaxNumberOfWheels = 18;
}
Strings intended for logging or tracing are exempt from this rule. Literals are allowed when their meaning is clear from the context, and not subject to future changes, For example:
mean = (a + b) / 2;// okay
WaitMilliseconds(waitTimeInSeconds * 1000); // clear enough
If the value of one constant depends on the value of another, attempt to make this explicit in the code.
public class SomeSpecialContainer
{
public const int MaxItems = 32;
public const int HighWaterMark = 3 * MaxItems / 4; // at 75%
}
Note: An enumeration can often be used for certain types of symbolic constants.
Only use var as the result of a LINQ query, or if the type is very obvious from the same statement and using it would improve readability. So don't
var i = 3; // what type? int? uint? float?
var myfoo = MyFactoryMethod.Create("arg"); // Not obvious what base-class or
// interface to expect. Also difficult
// to refactor if you can't search for
// the class
Instead, use var like this:
var q = from order in orders where order.Items > 10 and order.TotalValue > 1000;
var repository = new RepositoryFactory.Get();
var list = new ReadOnlyCollection();
In all of three above examples it is clear what type to expect. For a more detailed rationale about the advantages and disadvantages of using var, read Eric Lippert's Uses and misuses of implicit typing.
Avoid the C and Visual Basic styles where all variables have to be defined at the beginning of a block, but rather define and initialize each variable at the point where it is needed.
Don't use confusing constructs like the one below:
var result = someField = GetSomeMethod();
Instead of:
var startInfo = new ProcessStartInfo("myapp.exe");
startInfo.StandardOutput = Console.Output;
startInfo.UseShellExecute = true;
Use Object Initializers:
var startInfo = new ProcessStartInfo("myapp.exe")
{
StandardOutput = Console.Output,
UseShellExecute = true
};
Similarly, instead of:
var countries = new List();
countries.Add("Netherlands");
countries.Add("United States");
Use collection or dictionary initializers:
var countries = new List { "Netherlands", "United States" };
It is usually bad style to compare a bool-type expression to true or false. For example:
while (condition == false)// wrong; bad style
while (condition != true)// also wrong
while (((condition == true) == true) == true)// where do you stop?
while (condition)// OK
Updating the loop variable within the loop body is generally considered confusing, even more so if the loop variable is modified in more than one place.
for (int index = 0; index < 10; ++index)
{
if (_some condition_)
{
index = 11; // Wrong! Use 'break' or 'continue' instead.
}
}
A method that nests loops is more difficult to understand than one with only a single loop. In fact, in most cases nested loops can be replaced with a much simpler LINQ query that uses the from keyword twice or more to join the data.
Please note that this also avoids possible confusion in statements of the form:
if (b1) if (b2) Foo(); else Bar(); // which 'if' goes with the 'else'?
// The right way:
if (b1)
{
if (b2)
{
Foo();
}
else
{
Bar();
}
}
Add a descriptive comment if the default block is supposed to be empty. Moreover, if that block is not supposed to be reached throw an InvalidOperationException to detect future changes that may fall through the existing cases. This ensures better code, because all paths the code can travel have been thought about.
void Foo(string answer)
{
switch (answer)
{
case "no":
{
Console.WriteLine("You answered with No");
break;
}
case "yes":
{
Console.WriteLine("You answered with Yes");
break;
}
default:
{
// Not supposed to end up here.
throw new InvalidOperationException("Unexpected answer " + answer);
}
}
}
For example:
void Foo(string answer)
{
if (answer == "no")
{
Console.WriteLine("You answered with No");
}
else if (answer == "yes")
{
Console.WriteLine("You answered with Yes");
}
else
{
// What should happen when this point is reached? Ignored? If not,
// throw an InvalidOperationException.
}
}
One entry, one exit is a sound principle and keeps control flow readable. However, if the method is very small and complies with guideline AV1500 then multiple return statements may actually improve readability over some central boolean flag that is updated at various points.
Express your intentions directly. For example, rather than:
bool pos;
if (val > 0)
{
pos = true;
}
else
{
pos = false;
}
write:
bool pos = (val > 0);// initialization
Or instead of:
string result;
if (someString != null)
{
result = someString;
}
else
{
result = "Unavailable";
}
return result;
write:
return someString ?? "Unavailable";
Consider the following example:
if (member.HidesBaseClassMember && (member.NodeType != NodeType.InstanceInitializer))
{
// do something
}
In order to understand what this expression is about, you need to analyze its exact details and all of its possible outcomes. Obviously, you can add an explanatory comment on top of it, but it is much better to replace this complex expression with a clearly named method:
if (NonConstructorMemberUsesNewKeyword(member))
{
// do something
}
private bool NonConstructorMemberUsesNewKeyword(Member member)
{
return
(member.HidesBaseClassMember &&
(member.NodeType != NodeType.InstanceInitializer)
}
You still need to understand the expression if you are modifying it, but the calling code is now much easier to grasp.
This guideline only applies to overloads that are intended to provide optional arguments. Consider, for example, the following code snippet:
public class MyString
{
private string someText;
public int IndexOf(string phrase)
{
return IndexOf(phrase, 0);
}
public int IndexOf(string phrase, int startIndex)
{
return IndexOf(phrase, startIndex, someText.Length - startIndex);
}
public virtual int IndexOf(string phrase, int startIndex, int count)
{
return someText.IndexOf(phrase, startIndex, count);
}
}
The class MyString provides three overloads for the IndexOf method, but two of them simply call the one with one more parameter. Notice that the same rule applies to class constructors; implement the most complete overload and call that one from the other overloads using the this() operator. Also notice that the parameters with the same name should appear in the same position in all overloads.
Important: If you also want to allow derived classes to override these methods, define the most complete overload as a protected virtual method that is called by all overloads.
The only valid reason for using C# 4.0's optional arguments is to replace the example from rule AV1551 with a single method like:
public virtual int IndexOf(string phrase, int startIndex = 0, int count = 0)
{
return someText.IndexOf(phrase, startIndex, count);
}
If the optional parameter is a reference type then it can only have a default value of null. But since strings, lists and collections should never be null according to rule AV1235, you must use overloaded methods instead.
Note: The default values of the optional parameters are stored at the caller side. As such, changing the default value without recompiling the calling code will not apply the new default value properly.
Note: When an interface method defines an optional parameter, its default value is not considered during overload resolution unless you call the concrete class through the interface reference. See this post by Eric Lippert for more details.
C# 4.0's named arguments have been introduced to make it easier to call COM components that are known for offering many optional parameters. If you need named arguments to improve the readability of the call to a method, that method is probably doing too much and should be refactored.
Exception: The only exception where named arguments improve readability is when calling a method of some code base you don't control that has a bool parameter, like this:
object[] myAttributes = type.GetCustomAttributes(typeof(MyAttribute), inherit: false);
If you create a method with more than three parameters, use a structure or class to pass multiple arguments, as explained in the Specification design pattern. In general, the fewer the parameters, the easier it is to understand the method. Additionally, unit testing a method with many parameters requires many scenarios to test.
They make code less understandable and might cause people to introduce bugs. Instead, return compound objects.
Consider the following method signature:
public Customer CreateCustomer(bool platinumLevel) {}
On first sight this signature seems perfectly fine, but when calling this method you will lose this purpose completely:
Customer customer = CreateCustomer(true);
Often, a method taking such a flag is doing more than one thing and needs to be refactored into two or more methods. An alternative solution is to replace the flag with an enumeration.
Never use a parameter as a convenient variable for storing temporary state. Even though the type of your temporary variable may be the same, the name usually does not reflect the purpose of the temporary variable.
If you use as to obtain a certain interface reference from an object, always ensure that this operation does not return null. Failure to do so may cause a NullReferenceException at a much later stage if the object did not implement that interface. If you are sure the object is of a certain type, use the is operator instead.
Never check in code that is commented out. Instead, use a work item tracking system to keep track of some work to be done. Nobody knows what to do when they encounter a block of commented-out code. Was it temporarily disabled for testing purposes? Was it copied as an example? Should I delete it?