styleguide

C# at Google Style Guide

This style guide is for C# code developed internally at Google, and is the default style for C# code at Google. It makes stylistic choices that conform to other languages at Google, such as Google C++ style and Google Java style.

Formatting guidelines

Naming rules

Naming rules follow Microsoft’s C# naming guidelines. Where Microsoft’s naming guidelines are unspecified (e.g. private and local variables), rules are taken from the CoreFX C# coding guidelines

Rule summary:

Code

Files

Organization

Whitespace rules

Developed from Google Java style.

Example

using System;                                       // `using` goes at the top, outside the
                                                    // namespace.

namespace MyNamespace {                             // Namespaces are PascalCase.
                                                    // Indent after namespace.
  public interface IMyInterface {                   // Interfaces start with 'I'
    public int Calculate(float value, float exp);   // Methods are PascalCase
                                                    // ...and space after comma.
  }

  public enum MyEnum {                              // Enumerations are PascalCase.
    Yes,                                            // Enumerators are PascalCase.
    No,
  }

  public class MyClass {                            // Classes are PascalCase.
    public int Foo = 0;                             // Public member variables are
                                                    // PascalCase.
    public bool NoCounting = false;                 // Field initializers are encouraged.
    private class Results {
      public int NumNegativeResults = 0;
      public int NumPositiveResults = 0;
    }
    private Results _results;                       // Private member variables are
                                                    // _camelCase.
    public static int NumTimesCalled = 0;
    private const int _bar = 100;                   // const does not affect naming
                                                    // convention.
    private int[] _someTable = {                    // Container initializers use a 2
      2, 3, 4,                                      // space indent.
    }

    public MyClass() {
      _results = new Results {
        NumNegativeResults = 1,                     // Object initializers use a 2 space
        NumPositiveResults = 1,                     // indent.
      };
    }

    public int CalculateValue(int mulNumber) {      // No line break before opening brace.
      var resultValue = Foo * mulNumber;            // Local variables are camelCase.
      NumTimesCalled++;
      Foo += _bar;

      if (!NoCounting) {                            // No space after unary operator and
                                                    // space after 'if'.
        if (resultValue < 0) {                      // Braces used even when optional and
                                                    // spaces around comparison operator.
          _results.NumNegativeResults++;
        } else if (resultValue > 0) {               // No newline between brace and else.
          _results.NumPositiveResults++;
        }
      }

      return resultValue;
    }

    public void ExpressionBodies() {
      // For simple lambdas, fit on one line if possible, no brackets or braces required.
      Func<int, int> increment = x => x + 1;

      // Closing brace aligns with first character on line that includes the opening brace.
      Func<int, int, long> difference1 = (x, y) => {
        long diff = (long)x - y;
        return diff >= 0 ? diff : -diff;
      };

      // If defining after a continuation line break, indent the whole body.
      Func<int, int, long> difference2 =
          (x, y) => {
            long diff = (long)x - y;
            return diff >= 0 ? diff : -diff;
          };

      // Inline lambda arguments also follow these rules. Prefer a leading newline before
      // groups of arguments if they include lambdas.
      CallWithDelegate(
          (x, y) => {
            long diff = (long)x - y;
            return diff >= 0 ? diff : -diff;
          });
    }

    void DoNothing() {}                             // Empty blocks may be concise.

    // If possible, wrap arguments by aligning newlines with the first argument.
    void AVeryLongFunctionNameThatCausesLineWrappingProblems(int longArgumentName,
                                                             int p1, int p2) {}

    // If aligning argument lines with the first argument doesn't fit, or is difficult to
    // read, wrap all arguments on new lines with a 4 space indent.
    void AnotherLongFunctionNameThatCausesLineWrappingProblems(
        int longArgumentName, int longArgumentName2, int longArgumentName3) {}

    void CallingLongFunctionName() {
      int veryLongArgumentName = 1234;
      int shortArg = 1;
      // If possible, wrap arguments by aligning newlines with the first argument.
      AnotherLongFunctionNameThatCausesLineWrappingProblems(shortArg, shortArg,
                                                            veryLongArgumentName);
      // If aligning argument lines with the first argument doesn't fit, or is difficult to
      // read, wrap all arguments on new lines with a 4 space indent.
      AnotherLongFunctionNameThatCausesLineWrappingProblems(
          veryLongArgumentName, veryLongArgumentName, veryLongArgumentName);
    }
  }
}

C# coding guidelines

Constants

IEnumerable vs IList vs IReadOnlyList

Generators vs containers

Property styles

Expression body syntax

For example:

int SomeProperty => _someProperty

Structs and classes:

Lambdas vs named methods

Field initializers

Extension methods

ref and out

LINQ

Array vs List

Folders and file locations

Use of tuple as a return type

String interpolation vs String.Format() vs String.Concat vs operator+

using

Object Initializer syntax

For example:

var x = new SomeClass {
  Property1 = value1,
  Property2 = value2,
};

Namespace naming

Default values/null returns for structs

Removing from containers while iterating

C# (like many other languages) does not provide an obvious mechanism for removing items from containers while iterating. There are a couple of options:

Calling delegates

The var keyword

Attributes

Argument Naming

Derived from the Google C++ style guide.

When the meaning of a function argument is nonobvious, consider one of the following remedies:

Consider the following example:

// Bad - what are these arguments?
DecimalNumber product = CalculateProduct(values, 7, false, null);

versus:

// Good
ProductOptions options = new ProductOptions();
options.PrecisionDecimals = 7;
options.UseCache = CacheUsage.DontUseCache;
DecimalNumber product = CalculateProduct(values, options, completionDelegate: null);
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