D Programming Language
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# The D Style

The D Style is a set of style conventions for writing D programs. The D Style is not enforced by the compiler. It is purely cosmetic and a matter of choice. Adhering to the D Style, however, will make it easier for others to work with your code and easier for you to work with others' code. The D Style can form the starting point for a project style guide customized for your project team.

Submissions to Phobos and other official D source code will follow these guidelines.

### Whitespace

- One statement per line.
- Use spaces instead of hardware tabs.
- Each indentation level will be four columns.

### Comments

- Use // comments to document a single line:

      statement;  // comment
      statement;  // comment

- Use block comments to document a multiple line block of statements:

      /* comment
       * comment
       */
       statement;
       statement;

- Use version (none) to ‘comment out’ a piece of trial code that is syntactically valid:

        version (none)
        {
          /* comment
           * comment
           */
           statement;
           statement;
        }

  It can be turned on with version(all):

        version (all)
        {
          /* comment
           * comment
           */
           statement;
           statement;
        }

- Use nesting comments to ‘comment out’ a piece of syntactically invalid code:

      /+++++
          /* comment
           * comment
           */
           { statement;
             statement;
       +++++/

### Naming Conventions

General
  Unless listed otherwise below, names should be camelCased (this includes all variables). So, names formed by joining multiple words have each word other than the first word capitalized. Also, names do not begin with an underscore ‘_’ unless they are private.

      int myFunc();
      string myLocalVar;

Modules
  Module and package names should be all lowercase, and only contain the characters [a..z][0..9][_]. This avoids problems when dealing with case-insensitive file systems.

      import std.algorithm;

Classes, Structs, Unions, Enums, Templates
  The names of user-defined types should be PascalCased, which is the same as camelCased except that the first letter is uppercase.

      class Foo;
      struct FooAndBar;

  An exception is that eponymous templates that return a value instead of a type should not be capitalized, as they are conceptually more similar to functions.

      template GetSomeType(T) { alias T GetSomeType; }
      template isSomeType(T) { enum isSomeType = is(T == SomeType); }

Functions
  Function names should be camelCased, so their first letter is lowercase. This includes properties and member functions.

      int done();
      int doneProcessing();

Constants
  The names of constants should be camelCased just like normal variables.

      enum secondsPerMinute = 60;
      immutable hexDigits = "0123456789ABCDEF";

Enum members
  The members of enums should be camelCased, so their first letter is lowercase.

      enum Direction { bwd, fwd, both }
      enum OpenRight { no, yes }

Keywords
  If a name would conflict with a keyword, and it is desirable to use the keyword rather than pick a different name, a single underscore ‘_’ should be appended to it. Names should not be capitalized differently in order to avoid conflicting with keywords.

      enum Attribute { nothrow_, pure_, safe }

Acronyms
  When acronyms are used in symbol names, all letters in the acronym should have the same case. So, if the first letter in the acronym is lowercase, then all of the letters in the acronym are lowercase, and if the first letter in the acronym is uppercase, then all of the letters in the acronym are uppercase.

      class UTFException;
      ubyte asciiChar;

### Meaningless Type Aliases

Things like:

    alias void VOID;
    alias int INT;
    alias int* pint;

should be avoided.

### Declaration Style

Since the declarations are left-associative, left justify them:

    int[] x, y; // makes it clear that x and y are the same type
    int** p, q; // makes it clear that p and q are the same type

to emphasize their relationship. Do not use the C style:

    int []x, y; // confusing since y is also an int[]
    int **p, q; // confusing since q is also an int**

### Operator Overloading

Operator overloading is a powerful tool to extend the basic types supported by the language. But being powerful, it has great potential for creating obfuscated code. In particular, the existing D operators have conventional meanings, such as ‘+’ means ‘add’ and ‘<<’ means ‘shift left’. Overloading operator ‘+’ with a meaning different from ‘add’ is arbitrarily confusing and should be avoided.

### Hungarian Notation

Using hungarian notation to denote the type of a variable is a bad idea. However, using notation to denote the purpose of a variable (that cannot be expressed by its type) is often a good practice.

### Properties

Functions should be property functions whenever appropriate. In particular, getters and setters should generally be avoided in favor of property functions. And in general, whereas functions should be verbs, properties should be nouns, just like if they were member variables. Getter properties should not alter state.

### Documentation

All public declarations will be documented in Ddoc format.

### Unit Tests

As much as practical, all functions will be exercised by unit tests using unittest blocks immediately following the function to be tested. Every path of code should be executed at least once, verified by the code coverage analyzer.

## Additional Requirements for Phobos

In general, this guide does not try to recommend or require that code conform to any particular formatting guidelines. The small section on whitespace at the top contains its only formatting guidelines. However, for Phobos and other official D source code, there are two additional requirements:

- Braces should be on their own line. There are a few exceptions to this (such as when declaring lambda functions), but with any normal function block or type definition, the braces should be on their own line.

    void func(int param)
    {
        if(param < 0)
        {
            ...
        }
        else
        {
            ...
        }
    }

- Lines have a soft limit of 80 characters and a hard limit of 120 characters. This means that most lines of code should be no longer than 80 characters long but that they can exceed 80 characters when appropriate. However, they can never exceed 120 characters.

We are not necessarily recommending that all code follow these two rules. They're both likely to be controversial in any discussion on coding standards. However, they are required in submissions to Phobos and other official D source code.

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