coding-style.md

C# Coding Style

The general rule we follow is "use Visual Studio defaults". To enforce this, we make use of an .editorconfig file, and CodeMaid with some rules exported.

Specific Rules

1. We use Allman style braces, where each brace begins on a new line. A single line statement block can go without braces but the block must be properly indented on its own line and it must not be nested in other statement blocks that use braces (See issue 381 for examples).
2. We use four spaces of indentation (no tabs).
3. We use _camelCase for internal and private fields and use readonly where possible. Prefix instance fields with _, static fields with s_ and thread static fields with t_. When used on static fields, readonly should come after static (i.e. static readonly not readonly static).
4. We avoid this. unless absolutely necessary.
5. We always specify the visibility, even if it's the default (i.e. private string _foo not string _foo). Visibility should be the first modifier (i.e. public abstract not abstract public).
6. Namespace imports should be specified at the top of the file, outside of namespace declarations and should be sorted alphabetically.
7. Avoid more than one empty line at any time. For example, do not have two blank lines between members of a type.
8. Avoid spurious free spaces. For example avoid if (someVar == 0)..., where the dots mark the spurious free spaces. Consider enabling "View White Space (Ctrl+E, S)" if using Visual Studio, to aid detection.
9. If a file happens to differ in style from these guidelines (e.g. private members are named m_member rather than _member), the existing style in that file takes precedence.
10. We only use var when it's obvious what the variable type is (i.e. var stream = new FileStream(...) not var stream = OpenStandardInput()).
11. We use language keywords instead of BCL types (i.e. int, string, float instead of Int32, String, Single, etc) for both type references as well as method calls (i.e. int.Parse instead of Int32.Parse). See issue 391 for examples.
12. We use PascalCasing to name all our constant local variables and fields. The only exception is for interop code where the constant value should exactly match the name and value of the code you are calling via interop.
13. We use nameof(...) instead of "..." whenever possible and relevant.
14. Fields should be specified at the top within type declarations.
15. When including non-ASCII characters in the source code use Unicode escape sequences (\uXXXX) instead of literal characters. Literal non-ASCII characters occasionally get garbled by a tool or editor.

For non code files (e.g. xml, json, etc.) our current best guidance is consistency. When editing files, keep new code and changes consistent with the style in the files. For new files, it should conform to the style for that component. Last, if there's a completely new component, anything that is reasonably broadly accepted is fine.

Example Files

ObservableLinkedList`1.cs:

using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.Specialized;
using System.ComponentModel;
using System.Diagnostics;
using Microsoft.Win32;

namespace System.Collections.Generic
{
    public partial class ObservableLinkedList<T> : INotifyCollectionChanged, INotifyPropertyChanged
    {
        private ObservableLinkedListNode<T> _head;
        private int _count;

        public ObservableLinkedList(IEnumerable<T> items)
        {
            if (items == null)
            {
                throw new ArgumentNullException(nameof(items));
            }

            foreach (T item in items)
            {
                AddLast(item);
            }
        }

        public event NotifyCollectionChangedEventHandler CollectionChanged;

        public int Count => _count;

        public ObservableLinkedListNode AddLast(T value) 
        {
            var newNode = new LinkedListNode<T>(this, value);

            InsertNodeBefore(_head, node);
        }

        protected virtual void OnCollectionChanged(NotifyCollectionChangedEventArgs e)
        {
            NotifyCollectionChangedEventHandler handler = CollectionChanged;
            if (handler != null)
            {
                handler(this, e);
            }
        }

        private void InsertNodeBefore(LinkedListNode<T> node, LinkedListNode<T> newNode)
        {
           ...
        }
        
        ...
    }
}

ObservableLinkedList`1.ObservableLinkedListNode.cs:

using System;

namespace System.Collections.Generics
{
    partial class ObservableLinkedList<T>
    {
        public class ObservableLinkedListNode
        {
            private readonly ObservableLinkedList<T> _parent;
            private readonly T _value;

            internal ObservableLinkedListNode(ObservableLinkedList<T> parent, T value)
            {
                Debug.Assert(parent != null);

                _parent = parent;
                _value = value;
            }
            
            public T Value => _value;
        }

        ...
    }
}