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For other important guidance, see also:

Naming Conventions

  1. Use Pascal casing for type, method names, and constants:

    public class SomeClass
    {
        private const int DefaultSize = 100;
         
        public void SomeMethod()
        {
             …
        }
    }
  2. Use camel casing for local variable names and method arguments:

    public void SomeMethod(int someNumber)
    {
        int number;
        …
    }
  3. Prefix interfaces with I:

    public interface ISomethingProvider
    {
        …
    }
  4. Suffix interface implementations with the non-prefixed interface name:

    public class ThisSomethingProvider : ISomethingProvider
    {
        …
    }
  5. Prefix all fields with an underscore (_). If a file happens to differ in style from these guidelines, the existing style in that file takes precedence:

    public class SomeClass
    {
        private ISomethingProvider _thisSomethingProvider;
    }
  6. Name methods using a verb or verb-object pair (unless implementing a fluent API):

    public decimal CalculateTax(decimal amount)
    {
        …
    }
  7. You may use single-character or mnemonic variable names in the following scenarios:

    1. In for loops where it is a common convention to use variables like i , j , and k .

    2. In LINQ expressions where it is a common convention to use variables like x or a mnemonic for the item being represented (e.g., ssa  for an object of type StudentSchoolAssociation ).

  8. Do not abbreviate terms or use acronyms as this leads to usage inconsistency in the code and other application artifacts and reduces readability. Specifically, do not abbreviate "EducationOrganization" as “EdOrg” or “LocalEducationAgency” as “Lea”.

    1. Exceptions: well-known terms such as ODS, API, Id, msg, max, min, JSON, and so forth.

  9. Name abstract classes using a suffix of Base (e.g., EdFiControllerBase).

  10. Name extension classes and files by the type being extended.

    ByteArrayExtensions.cs
    public static class ByteArrayExtensions
    {
        public static int ToInt32(this byte[] input) => BitConverter.ToInt32(input, 0);
    
        public static long ToInt64(this byte[] input) => BitConverter.ToInt64(input, 0);
    
        public static string ToHexString(this byte[] input) => BitConverter.ToString(input).Replace("-", "");
    }

See also C# Best Practices: Naming Conventions

Formatting

  1. Use Allman style braces where each brace begins on a new line and use consistent style.

    // Good
    if (a == b)
    {
        c = d;
    }
    
    // Bad
    if (a == b) {
    	c = d;
    }
    
    // Bad - inconsistent style
    if (a == b)
    	c = d;
    else
    {
    	c = e;
    }
  2. Do not add blank lines between sets of closing braces.

    if (a == b)
    {
        if (c == d)
        {
            if (e == f)
            {
                DoSomething();
            }
        }
     
    } // The blank line above this brace should be removed.
  3. Include blank lines after closing braces as long as the next statement isn't part of a continuing language construct (e.g., if / else, try / catch / finally).

    // Good
    public static string ToCamelCase(this string text)
    {
        if (string.IsNullOrWhiteSpace(text))
        {
            return text;
        }
     
        return char.ToLower(text[0]) + text.Substring(1);
    }
     
    // Bad
    public static string ToCamelCase(this string text)
    {
        if (string.IsNullOrWhiteSpace(text))
        {
            return text;
        }
        return char.ToLower(text[0]) + text.Substring(1);
    } 
  4. Use parentheses to make clauses in an expression apparent, as shown in the following code:

    if ((val1 > val2) && (val1 > val3))
    {
        // Take appropriate action.
    }
  5. When building multi-line conditional statements, put the conditional operator at the beginning of each line.

    // Good
    public bool IsEmpty()
    {
        return
            !(EducationOrganizationId.HasValue || StateEducationAgencyId.HasValue
              || EducationServiceCenterId.HasValue || LocalEducationAgencyId.HasValue
              || SchoolId.HasValue || EducationOrganizationNetworkId.HasValue)
              && string.IsNullOrWhiteSpace(StaffUniqueId)
              && string.IsNullOrWhiteSpace(StudentUniqueId)
              && string.IsNullOrWhiteSpace(ParentUniqueId)
              && string.IsNullOrWhiteSpace(Namespace)
              && string.IsNullOrWhiteSpace(AssessmentFamilyTitle)
              && string.IsNullOrWhiteSpace(AssessmentTitle);
    }
     
    // Bad
    public bool IsEmpty()
    {
        return
            !(EducationOrganizationId.HasValue || StateEducationAgencyId.HasValue
              || EducationServiceCenterId.HasValue || LocalEducationAgencyId.HasValue
              || SchoolId.HasValue || EducationOrganizationNetworkId.HasValue) &&
              string.IsNullOrWhiteSpace(StaffUniqueId) &&
              string.IsNullOrWhiteSpace(StudentUniqueId) &&
              string.IsNullOrWhiteSpace(ParentUniqueId) &&
              string.IsNullOrWhiteSpace(Namespace) &&
              string.IsNullOrWhiteSpace(AssessmentFamilyTitle) &&
              string.IsNullOrWhiteSpace(AssessmentTitle);
    }
  6. Put auto-properties on a single line.

    // Good
    public int Age { get; set; }
     
    // Bad
    public int Age
    {
         get;
         set;
    }
  7. Bring base or this constructors onto a separate line (indented).

    public NotFoundException(string message, string typeName, string identifier)
        : base(message)
    {
        TypeName = typeName;
        Identifier = identifier;
    }
  8. Constructors with no bodies can be shortened to one line.

    public NotFoundException() {}
      
    public NotFoundException(string message)
        : base(message) {}
  9. Bring constraints for generic types onto separate lines (indented).

    public abstract class EdFiControllerBase<TResource, TEntityInterface, TAggregateRoot, TGetByKeyRequest, TPutRequest, TPostRequest, TDeleteRequest> : ApiController
        where TResource : IHasIdentifier, IHasETag, new()
        where TEntityInterface : class
        where TAggregateRoot : class, IHasIdentifier, new()
        where TPutRequest : TResource
        where TPostRequest : TResource
        where TDeleteRequest : IHasIdentifier
    {
        …
    }
  10. Namespace imports should be specified at the top of the file, outside of namespace declarations and should be sorted alphabetically, with System. namespaces at the top.
  11. Class artifacts should be organized as follows:
    1. Fields (primarily holding injected dependencies).
    2. Constructor(s).
    3. Public members (properties and methods).
    4. Define property-backing fields immediately before the property.

      private IEnumerable<Student> _students;
       
      public IEnumerable<Student> Students
      {
          get { return _students; }
      }
    5. Define non-shared supporting methods immediately following the method they were introduced to support, or use a local method.

      public void DoSomethingInteresting()
      {
          …
          int something = GetSomething();
          …
          int anotherThing = GetAnotherThing();
      }
       
      private int GetSomething()
      {
         // ...
      }
       
      private int GetAnotherThing()
      {
         // ...
      }
      
      // Local method variant
      public void DoSomethingCompletelyDifferent()
      {
          int something = GetSomething();
          // ...
      
      	int GetSomething()
      	{
          	// ...
      	}
      }

Data Types

  1. Use idiomatic C# types instead of .NET Framework types.

    Idiomatic  (tick)Framework (error)
    stringString
    objectObject
    intInt32
    doubleDouble
  2. In general, use int rather than unsigned types. The use of int is common throughout C#, and it is easier to interact with other libraries when you use int.
  3. String Data Type
    1. Use string interpolation to concatenate short strings, as shown in the following code:

      string displayName = $"{nameList[n].LastName}, {nameList[n].FirstName}";


    2. To append strings in loops, especially when you are working with large amounts of text, use a StringBuilder object.

      var phrase = "lalalalalalalalalalalalalalalalalalalalalalalala";
      var manyPhrases = new StringBuilder();
      for (var i = 0; i < 10000; i++)
      {
          manyPhrases.Append(phrase);
      }
      //Console.WriteLine("tra" + manyPhrases);

    3. Use case-insensitive checks rather than converting the casing of strings for case-sensitive comparison.

      string value1 = "Bob";
      string value2 = "BoB";
       
      // Good
      if (value1.Equals(value2, StringComparison.InvariantCultureIgnoreCase))
      {
          return true;
      }
       
      // Bad
      if (value1.ToLower() == value2.ToLower())
      {
          return true;
      }
  4. Implicitly typed local variables are generally preferred over explicit typing, unless the programmer or reviewer feels that an explicit type is a significant readability improvement.

    // When the type of a variable is clear from the context, use var
    // in the declaration.
    var var1 = "This is clearly a string.";
    var var2 = 27;
    var var3 = Convert.ToInt32(Console.ReadLine());
    
    // IntelliSense will prevent you from misusing `var4`, even though
    // the reader cannot see the type in plain text.
    int var4 = ExampleClass.ResultSoFar();
  5. Do not rely on the variable name to specify the type of the variable. It might not be correct.

    // Naming the following variable inputInt is misleading.
    // It is a string.
    var inputInt = Console.ReadLine();
    Console.WriteLine(inputInt);


  6. Do not use the C# dynamic type.

Initialization

  1. Arrays: Use the concise syntax when you initialize arrays on the declaration line.

    // Preferred syntax. Note that you cannot use var here instead of string[].
    string[] vowels1 = { "a", "e", "i", "o", "u" };
    
    // If you use explicit instantiation, you can use var.
    var vowels2 = new string[] { "a", "e", "i", "o", "u" };
    
    // If you specify an array size, you must initialize the elements one at a time.
    var vowels3 = new string[5];
    vowels3[0] = "a";
    vowels3[1] = "e";
    // And so on.
  2. New Operator: Use the concise form of object instantiation, with implicit typing, as shown in the following declaration:

    var instance1 = new ExampleClass();
    
    // The previous line is equivalent to the following declaration.
    ExampleClass instance2 = new ExampleClass();

  3. Use object initializers to simplify object creation.

    // Good
    var claims = new List<Claims>
        {
            new Claim("name1", "value1"),
            new Claim("name2", "value2"),
        };
     
    var studentById = new Dictionary<int, Student>
        {
            { 123456, new Student { Name = "John Doe", Age = 17} },
            { 234567, new Student { Name = "Jane Doe", Age = 16} },
        };
     
    // Bad
    var claims = new List<Claims>();
    claims.Add(new Claim("name1", "value1"));
    claims.Add(new Claim("name2", "value2"));
     
    // Even Worse
    var studentById = new Dictionary<int, Student>();
     
    var student1 = new Student();
    student1.Name = "John Doe";
    student1.Name = 17;
     
    var student2 = new Student();
    student2.Name = "Jane Doe";
    student2.Name = 16;
     
    studentById.Add(123456, student1);
    studentById.Add(234567, student2);

Exception Handling

  1. Use a try-catch statement for most exception handling.

    static string GetValueFromArray(string[] array, int index)
    {
        try
        {
            return array[index];
        }
        catch (System.IndexOutOfRangeException ex)
        {
            Console.WriteLine("Index is out of range: {0}", index);
            throw;
        }
    }

  2. Simplify your code by using the C# using statement. If you have a try-finally statement in which the only code in the finally block is a call to the Dispose method, use a using statement instead.

    // This try-finally statement only calls Dispose in the finally block.
    Font font1 = new Font("Arial", 10.0f);
    try
    {
        byte charset = font1.GdiCharSet;
    }
    finally
    {
        if (font1 != null)
        {
            ((IDisposable)font1).Dispose();
        }
    }
    
    // You can do the same thing with a using statement.
    using (Font font2 = new Font("Arial", 10.0f))
    {
        byte charset = font2.GdiCharSet;
    }
  3. Define custom exception classes when you expect the exception to be explicitly handled somewhere else in your application. It's a lot more reliable to match an exception based on its type than by extracting information from the message.

See also C# Best Practices: Exception Handling.

Null Detection

Avoid surprise null reference exceptions by checking for null values before using an object reference:

  1. On public, protected, and internal method arguments:

    public void Something(Object obj)
    {
        if (obj == null)
    	{
            throw new ArgumentNullException(nameof(obj));
        }
    }
  2. On constructor arguments except when the constructor is invoked by the IoC container. In that case, we tend to trust that the container will not inject a null object. Thus this primarily relates to constructors that we expect to invoke directly in code.

    public class A
    {
        private readonly B _b;
     
        public A(B b)
    	{
            _b = b ?? throw new ArgumentNullException(nameof(b));
        }
    }
  3. When receiving a value from a dependency. You may be able to look at the dependency code and confirm that it does not right now return a null, but it is safer to assume that it can return a null value.

    public class A
    {
        private readonly ISomeInterface _b;
     
        public A(ISomeInterface b)
    	{
            _b = b;
        }
     
        public bool DoSomething()
    	{
           var c = _b.CallAMethod();
     
           if (c == null)
    	   {
               throw new InvalidOperationException("Cannot calculate value due to dependent object returning a null value unexpectedly");
           }
     
           return c.IsTrue;
        }
    }


    Alternately, if receiving a null value is acceptable, then be sure to handle it per the business requirements. Only do this if null is a real expected value. Otherwise, if null is not expected and you convert to a real value, that might be masking an underlying bug in the dependency.

    public class A
    {
        private readonly ISomeInterface _b;
     
        public A(ISomeInterface b)
        {
            _b = b;
        }
     
        public bool DoSomething()
        {
           var c = _b.CallAMethod();
     
           // Accept null values above, but treat as false
           return c?.IsTrue ?? false;
        }
    }

    This is an exceptional comment: it explains what the code is doing. In this case, it seems reasonable because the code is doing something unusual. The comment makes clear that it was quite intentional.

LINQ Queries

  1. The Alliance development teams generally prefer the Method Syntax over the Query Syntax for LINQ. Some older code does contain the Query Syntax; this can be changed opportunistically or left as is.
  2. Use meaningful names for query variables. The following example uses seattleCustomers for customers who are located in Seattle.

    var seattleCustomers = customers.Where(x => x.City == "Seattle")
                                    .Select(x => x.Name);

  3. Use aliases to make sure that property names of anonymous types are correctly capitalized, using Pascal casing.

    var seattleCustomers = customers.Join(distributors, 
    									  customer => customer.City, 
    									  distributor => distributor.City,
    									  (customer, distributor) => new { 
                                              Customer = customer,
                                              Distributor = distributor 
                                          });


  4. Rename properties when the property names in the result would be ambiguous. For example, if your query returns a customer name and a distributor ID, instead of leaving them as Name and Id in the result, rename them to clarify that Name is the name of a customer, and ID is the ID of a distributor.

    var seattleCustomers = customers.Join(distributors, 
    									  customer => customer.City, 
    									  distributor => distributor.City,
    									  (customer, distributor) => new {
                                              CustomerName = customer.Name,
                                              DistributorId = distributor.Id 
                                          });

  5. Use implicit typing in the declaration of query variables and range variables.

    var seattleCustomers = customers.Where(x => x.City == "Seattle")
                                    .Select(x => x.Name);
  6. Use Where clauses before other query clauses to ensure that later query clauses operate on the reduced, filtered set of data.

    var seattleCustomers = customers.Where(x => x.City == "Seattle")
    			                     .OrderBy(x => x.Age)
                                     .Select(x);

Other Rules

  1. && and || Operators: To avoid exceptions and increase performance by skipping unnecessary comparisons, use && instead of & and || instead of | when you perform comparisons, as shown in the following example.

    Console.Write("Enter a dividend: ");
    var dividend = Convert.ToInt32(Console.ReadLine());
    
    Console.Write("Enter a divisor: ");
    var divisor = Convert.ToInt32(Console.ReadLine());
    
    // If the divisor is 0, the second clause in the following condition
    // causes a run-time error. The && operator short circuits when the
    // first expression is false. That is, it does not evaluate the
    // second expression. The & operator evaluates both, and causes
    // a run-time error when divisor is 0.
    if ((divisor != 0) && (dividend / divisor > 0))
    {
        Console.WriteLine("Quotient: {0}", dividend / divisor);
    }
    else
    {
        Console.WriteLine("Attempted division by 0 ends up here.");
    }
  2. Always use explicit scope.

    // Good
    public class Something
    {
        private const int MaximumAge = 100;
     
        public int Age { get; set; }
     
        public void SayHello()
        {
            Console.WriteLine("Hello.");
        }
    }
     
    // Bad
    class Something
    {
        const int MaximumAge = 100;
     
        int Age { get; set; }
     
        void SayHello()
        {
            Console.WriteLine("Hello.");
        }
    }
  3. Use string.Empty  rather than empty quotes ("") for empty strings. It clarifies true intent.
  4. Do not exceed about 20-30 lines of code in a single method. After that, refactor the method into smaller well-named methods. 
  5. When using local functions:

    1. Limit use of closure on variables from the enclosing method, as they can make it difficult to read and understand the overall method.

      public void Demonstration(string path)
      {
      	var pathComponents = input.Split('/');
      	// ...
      	// ...
      	
      	// Good
      	string First(IEnumerable<string> pathComponents)
      	{
      		if (pathComponents.Any())
      		{
      			return pathComponents.First();
      		}
      		throw new InvalidOperationException("Path does not contain any components");
      	}
      
      	// Bad
      	string First()
      	{
      		// Where did `pathComponents` come from?
      		if (pathComponents.Any())
      		// etc.
      	}
      }
    2. Limit local methods to only a few lines of code, and continue keeping the entire outer method to a reasonable length. Longer local methods are a code smell and make it more difficult to quickly understand the intent.
  6. Favor a coding style of "fail fast" (and also "exit fast"). If there is an exception to be thrown or a value to be returned with no further logic, perform that logic immediately rather than leaving it for an else clause.

    // Good
    public void SomeMethod(ISomethingProvider somethingProvider)
    {
        // Check for known failure condition and exit quickly
        if (somethingProvider == null)
            throw new ArgumentNullException("somethingProvider");
     
        var things = _somethingElseProvider.GetThoseThings();
        …
    }
     
    // Bad
    public void SomeMethod(ISomethingProvider somethingProvider)
    {
        if (somethingProvider != null)
        {
            var things = _somethingElseProvider.GetThoseThings();
            … // Lots of logic here that a maintainer has to scroll through.
        }
        else
        {
            // This should be moved to the top of the method
            throw new ArgumentNullException("somethingProvider");
        }
    }
  7. Do not use regions (i.e., #region).
  8. Avoid the use of the dynamic keyword, particularly in code that executes frequently. Dynamic dispatch is very expensive and is rarely actually needed.
  9. Avoid passing values around using KeyValuePair<TKey, TValue>, but if you do, use a name format like {keyName}And{valueName} to ease maintenance (e.g. use schoolIdAndName for an entry from a dictionary named schoolNameById).
  10. Use explicit property name on anonymous types, and place each property on a separate line.

    // Assuming there are a couple of objects being mapped into an anonymous type, call them "sourceA" and "sourceB", with various properties on them...
    
    // Avoid
    var a = { sourceA.Property1, sourceB.Property2 };
    
    // Instead use
    var a = {
        Property1 = sourceA.Property1,
        Property2 = sourceB.Property2
    };
  11. When using ReSharper, it may occasionally be appropriate to suppress a warning, for example when using snake-case naming convention on tests. Prefer suppressing messages using the comment syntax rather than [SuppressMessage] , e.g. // ReSharper disable InconsistentNaming. Except for this obvious case of test names, these suppression comments should include a statement of why ReSharper analysis is being disabled, and the code reviewer should carefully consider whether the comment is indeed warranted.


Portions of this document are based on the Microsoft C# Coding Conventions, which have been reproduced and modified under the terms of the Creative Commons Attribution 4.0 International license.

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