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D, also known as Dlang, is a multi-paradigmsystem programming language created by Walter Bright at Digital Mars and released in 2001. Andrei Alexandrescu joined the design and development effort in 2007. Though it originated as a re-engineering of C++, D is a distinct language. It has redesigned some core C++ features, while also sharing characteristics of other languages, notably Java, Python, Ruby, C#, and Eiffel.

The design goals of the language attempt to combine the performance and safety of compiled languages with the expressive power of modern dynamic languages. Idiomatic D code is commonly as fast as equivalent C++ code, while also being shorter.^[8] The language as a whole is not memory-safe,^[9] but does include optional attributes designed to check memory safety.^[10]

Type inference, automatic memory management and syntactic sugar for common types allow faster development, while bounds checking, design by contract features and a concurrency-aware type system help reduce the occurrence of bugs.^[11]

• 1Features
  • 1.1Programming paradigms
• 5Examples

Features[edit]

D is designed with lessons learned from practical C++ usage, rather than from a purely theoretical perspective. Although it uses many C and C++ concepts it also discards some, and is as such not compatible with C and C++ source code. D has, however, been constrained in its design by the rule that any code that is legal in both C and D should behave in the same way. D gained some features before C++ did, for example closures, anonymous functions, and compile time function execution. D adds to the functionality of C++ by also implementing design by contract, unit testing, true modules, garbage collection, first classarrays, associative arrays, dynamic arrays, array slicing, nested functions, lazy evaluation, and a re-engineered template syntax. D retains C++'s ability to perform low-level coding and to add inlineassembler. C++ multiple inheritance is replaced by Java-style single inheritance with interfaces and mixins. On the other hand, D's declaration, statement and expression syntax closely matches that of C++.

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The inline assembler typifies the differences between D and application languages like Java and C#. An inline assembler lets programmers enter machine-specific assembly code within standard D code, a method often used by system programmers to access the low-level features of the processor needed to run programs that interface directly with the underlying hardware, such as operating systems and device drivers.

D has built-in support for documentation comments, allowing automatic documentation generation.

Programming paradigms[edit]

D supports five main programming paradigms: imperative, object-oriented, metaprogramming, functional and concurrent (actor model).

Imperative[edit]

Imperative programming in D is almost identical to that in C. Functions, data, statements, declarations and expressions work just as they do in C, and the C runtime library may be accessed directly. On the other hand, some notable differences between D and C in the area of imperative programming include D's foreach loop construct, which allows looping over a collection, and nested functions, which are functions that are declared inside of another and may access the enclosing function's local variables.

Object-oriented[edit]

Object-oriented programming in D is based on a single inheritance hierarchy, with all classes derived from class Object. D does not support multiple inheritance; instead, it uses Java-style interfaces, which are comparable to C++'s pure abstract classes, and mixins, which separates common functionality from the inheritance hierarchy. D also allows the defining of static and final (non-virtual) methods in interfaces.

Metaprogramming[edit]

Metaprogramming is supported by a combination of templates, compile time function execution, tuples, and string mixins. The following examples demonstrate some of D's compile-time features.

Templates in D can be written in a more imperative style compared to the C++ functional style for templates. This is a regular function that calculates the factorial of a number:

Here, the use of static if, D's compile-time conditional construct, is demonstrated to construct a template that performs the same calculation using code that is similar to that of the function above:

In the following two examples, the template and function defined above are used to compute factorials. The types of constants need not be specified explicitly as the compiler infers their types from the right-hand sides of assignments:

This is an example of compile time function execution. Ordinary functions may be used in constant, compile-time expressions provided they meet certain criteria:

The std.string.format function performs printf-like data formatting (also at compile-time, through CTFE), and the 'msg' pragma displays the result at compile time:

String mixins, combined with compile-time function execution, allow generating D code using string operations at compile time. This can be used to parse domain-specific languages to D code, which will be compiled as part of the program:

Functional[edit]

D supports functional programming features such as function literals, closures, recursively-immutable objects and the use of higher-order functions. There are two syntaxes for anonymous functions, including a multiple-statement form and a 'shorthand' single-expression notation:^[8]

There are two built-in types for function literals, function, which is simply a pointer to a stack-allocated function, and delegate, which also includes a pointer to the surrounding environment. Type inference may be used with an anonymous function, in which case the compiler creates a delegate unless it can prove that an environment pointer is not necessary. Likewise, to implement a closure, the compiler places enclosed local variables on the heap only if necessary (for example, if a closure is returned by another function, and exits that function's scope). When using type inference, the compiler will also add attributes such as pure and nothrow to a function's type, if it can prove that they apply.

Other functional features such as currying and common higher-order functions such as map, filter, and reduce are available through the standard library modules std.functional and std.algorithm.

Alternatively, the above function compositions can be expressed using Uniform Function Call Syntax (UFCS) for more natural left-to-right reading:

Parallel[edit]

Concurrent[edit]

Memory management[edit]

Memory is usually managed with garbage collection, but specific objects may be finalized immediately when they go out of scope. Explicit memory management is possible using the overloaded operatorsnew and delete, and by simply calling C's malloc and free directly. Garbage collection can be controlled: programmers may add and exclude memory ranges from being observed by the collector, can disable and enable the collector and force either a generational or full collection cycle.^[12] The manual gives many examples of how to implement different highly optimized memory management schemes for when garbage collection is inadequate in a program.^[13]

SafeD[edit]

SafeD^[14]is the name given to the subset of D that can be guaranteed to be memory safe (no writes to memory that were not allocated or that have already been recycled). Functions marked @safe are checked at compile time to ensure that they do not use any features that could result in corruption of memory, such as pointer arithmetic and unchecked casts, and any other functions called must also be marked as @safe or @trusted. Functions can be marked @trusted for the cases where the compiler cannot distinguish between safe use of a feature that is disabled in SafeD and a potential case of memory corruption.^[15]

Interaction with other systems[edit]

C's application binary interface (ABI) is supported, as well as all of C's fundamental and derived types, enabling direct access to existing C code and libraries. D bindings are available for many popular C libraries. Additionally, C's standard library is a part of standard D.

Because C++ does not have a single standard ABI, D can only fully access C++ code that is written to the C ABI. The D parser understands an extern (C++) calling convention for limited linking to C++ objects.

On Microsoft Windows, D can access Component Object Model (COM) code.

History[edit]

Walter Bright decided to start working on a new language in 1999. D was first released in December 2001,^[1] and reached version 1.0 in January 2007.^[16] The first version of the language (D1) concentrated on the imperative, object oriented and metaprogramming paradigms,^[17] similar to C++.

Dissatisfied with Phobos, D's official runtime and standard library, members of the D community created an alternative runtime and standard library named Tango. The first public Tango announcement came within days of D 1.0's release.^[18] Tango adopted a different programming style, embracing OOP and high modularity. Being a community-led project, Tango was more open to contributions, which allowed it to progress faster than the official standard library. At that time, Tango and Phobos were incompatible due to different runtime support APIs (the garbage collector, threading support, etc.). This made it impossible to use both libraries in the same project. The existence of two libraries, both widely in use, has led to significant dispute due to some packages using Phobos and others using Tango.^[19]

In June 2007, the first version of D2 was released.^[2] The beginning of D2's development signalled the stabilization of D1; the first version of the language has been placed in maintenance, only receiving corrections and implementation bugfixes. D2 was to introduce breaking changes to the language, beginning with its first experimental const system. D2 later added numerous other language features, such as closures, purity, and support for the functional and concurrent programming paradigms. D2 also solved standard library problems by separating the runtime from the standard library. The completion of a D2 Tango port was announced in February 2012.^[20]

The release of Andrei Alexandrescu's book The D Programming Language on 12 June 2010 marked the stabilization of D2, which today is commonly referred to as just 'D'.

In January 2011, D development moved from a bugtracker / patch-submission basis to GitHub. This has led to a significant increase in contributions to the compiler, runtime and standard library.^[21]

In December 2011, Andrei Alexandrescu announced that D1, the first version of the language, would be discontinued on 31 December 2012.^[22] The final D1 release, D v1.076, was on 31 December 2012.^[23]

Code for the official D compiler, the Digital Mars D compiler by Walter Bright, was originally released under a custom license, qualifying as source available, but not conforming to the open source definition.^[24] In 2014 the compiler front-end was re-licensed as open source under the Boost Software License.^[3] This re-licensed code excluded the back-end, which had been partially developed at Symantec. On 7 April 2017, the entire compiler was made available under the Boost license after Symantec gave permission to re-license the back-end, too.^{[4][25][26][27]} On 21 June 2017, the D Language was accepted for inclusion in GCC.^[28]

Implementations[edit]

Most current D implementations compile directly into machine code for efficient execution.

• DMD – The Digital Mars D compiler by Walter Bright is the official D compiler; open sourced under the Boost Software License.^[3][4]
• GDC – A front-end for the GCC back-end, built using the open DMD compiler source code.^[29]
• LDC – A compiler based on the DMD front-end that uses LLVM as its compiler back-end. The first release-quality version was published on 9 January 2009.^[30] It supports version 2.0.^[31]
• D Compiler for .NET – A back-end for the D programming language 2.0 compiler.^[32][33] It compiles the code to Common Intermediate Language (CIL) bytecode rather than to machine code. The CIL can then be run via a Common Language Infrastructure (CLR) virtual machine.
• SDC – The Stupid D Compiler uses a custom front-end and LLVM as its compiler back-end. It is written in D and uses a scheduler to handle symbol resolution in order to elegantly handle the compile-time features of D. This compiler currently supports a limited subset of the language.^[34][35]

Development tools[edit]

Editors and integrated development environments (IDEs) supporting D include Eclipse, Microsoft Visual Studio, SlickEdit, Emacs, vim, SciTE, Smultron, TextMate, MonoDevelop, Zeus,^[36] and Geany among others.^[37]

• Eclipse plug-ins for D include: DDT^[38] and Descent (dead project).^[39]
• Visual Studio integration is provided by VisualD.^[40]
• Visual Studio Code integration with extensions as Dlang-Vscode^[41] or Code-D.^[42]
• Vim supports both syntax highlighting and code completion
• A bundle is available for TextMate, and the Code::Blocks IDE includes partial support for the language. However, standard IDE features such as code completion or refactoring are not yet available, though they do work partially in Code::Blocks (due to D's similarity to C).
• A plugin for Xcode 3 is available, D for Xcode, to enable D-based projects and development.^[43]
• An AddIn for MonoDevelop is available, named Mono-D.^[44]
• KDevelop (as well as its text editor backend, Kate) autocompletion plugin is available.^[45]
• Coedit, an open source IDE dedicated to D.^[46]

Open source D IDEs for Windows exist, some written in D, such as Poseidon,^[47] D-IDE,^[48] and Entice Designer.^[49]

D applications can be debugged using any C/C++ debugger, like GDB or WinDbg, although support for various D-specific language features is extremely limited. On Windows, D programs can be debugged using Ddbg, or Microsoft debugging tools (WinDBG and Visual Studio), after having converted the debug information using cv2pdb. The ZeroBUGS debugger for Linux has experimental support for the D language. Ddbg can be used with various IDEs or from the command line; ZeroBUGS has its own graphical user interface (GUI).

Examples[edit]

Example 1[edit]

This example program prints its command line arguments. The main function is the entry point of a D program, and args is an array of strings representing the command line arguments. A string in D is an array of characters, represented by char[] in D1, or immutable(char)[] in D2.

The foreach statement can iterate over any collection. In this case, it is producing a sequence of indexes (i) and values (arg) from the array args. The index i and the value arg have their types inferred from the type of the array args.

Example 2[edit]

The following shows several D capabilities and D design trade-offs in a very short program. It iterates over the lines of a text file named words.txt, which contains a different word on each line, and prints all the words that are anagrams of other words.

1. signs2words is a built-in associative array that maps dstring (32-bit / char) keys to arrays of dstrings. It is similar to defaultdict(list) in Python.
2. lines(File()) yields lines lazily, with the newline. It has to then be copied with idup to obtain a string to be used for the associative array values (the idup property of arrays returns an immutable duplicate of the array, which is required since the dstring type is actually immutable(dchar)[]). Built-in associative arrays require immutable keys.
3. The ~= operator appends a new dstring to the values of the associate dynamic array.
4. toLower, join and chomp are string functions that D allows the use of with a method syntax. The name of such functions is often very similar to Python string methods. The toLower converts a string to lower case, join(' ') joins an array of strings into a single string using a single space as separator, and chomp removes a newline from the end of the string if one is present.
5. The sort is an std.algorithm function that sorts the array in place, creating a unique signature for words that are anagrams of each other. The release() method on the return value of sort() is handy to keep the code as a single expression.
6. The second foreach iterates on the values of the associative array, it's able to infer the type of words.
7. key is assigned to an immutable variable, its type is inferred.
8. UTF-32dchar[] is used instead of normal UTF-8char[] otherwise sort() refuses to sort it. There are more efficient ways to write this program that use just UTF-8.

Uses[edit]

Notable organisations that use the D programming language for projects include Facebook,^[50]eBay,^[51] and Netflix.^[52]

D has been successfully used for AAA games,^[53] a JavaScript virtual machine,^[54][55] an operating systemkernel,^[56]GPU programming,^[57]web development,^[58][59]numerical analysis,^[60]GUI applications,^[61][62] and a passenger information system.^[63]

See also[edit]

References[edit]

1. ^ ^ab'D Change Log to Nov 7 2005'. D Programming Language 1.0. Digital Mars. Retrieved 1 December 2011.
2. ^ ^abc'Change Log – D Programming Language'. D Programming Language 2.0. D Language Foundation. Retrieved 28 May 2019.
3. ^ ^abc'dmd front end now switched to Boost license'. Retrieved 9 September 2014.
4. ^ ^abc'dmd Backend converted to Boost License'. 7 April 2017. Retrieved 9 April 2017.
5. ^'D 2.0 FAQ'. Retrieved 11 August 2015.
6. ^Alexandrescu, Andrei (2010). The D programming language (First ed.). Upper Saddle River, New Jersey: Addison-Wesley. p. 314. ISBN0321635361.
7. ^'Building assert() in Swift, Part 2: __FILE__ and __LINE__'. Retrieved 25 September 2014.
8. ^ ^ab'Expressions'. Digital Mars. Retrieved 27 December 2012.
9. ^'On: Ruminations on D: An Interview with Walter Bright'. Hacker News. 30 August 2016. 'It's close, and we're working to close the remaining gaps.'
10. ^'Memory-Safe-D-Spec'. D Language Foundation.
11. ^Andrei Alexandrescu (2 August 2010). Three Cool Things About D.
12. ^'std.gc'. D Programming Language 1.0. Digital Mars. Retrieved 6 July 2010.
13. ^'Memory Management'. D Programming Language 2.0. Digital Mars. Retrieved 17 February 2012.
14. ^Bartosz Milewski. 'SafeD – D Programming Language'. Retrieved 17 July 2014.
15. ^Steven Schveighoffer. 'How to Write @trusted Code in D'. Retrieved 4 January 2018.
16. ^'D Change Log'. D Programming Language 1.0. Digital Mars. Retrieved 11 January 2012.
17. ^'Intro'. D Programming Language 1.0. Digital Mars. Retrieved 1 December 2011.
18. ^'Announcing a new library'. Retrieved 15 February 2012.
19. ^'Wiki4D: Standard Lib'. Retrieved 6 July 2010.
20. ^'Tango for D2: All user modules ported'. Retrieved 16 February 2012.
21. ^Walter Bright. 'Re: GitHub or dsource?'. Retrieved 15 February 2012.
22. ^Andrei Alexandrescu. 'D1 to be discontinued on December 31, 2012'. Retrieved 31 January 2014.
23. ^'D Change Log'. D Programming Language 1.0. Digital Mars. Retrieved 31 January 2014.
24. ^'backendlicense.txt'. DMD source code. GitHub. Retrieved 5 March 2012.
25. ^'Reddit comment by Walter Bright'. Retrieved 9 September 2014.
26. ^D-Compiler-unter-freier-Lizenz on linux-magazin.de (2017, in German)
27. ^switch backend to Boost License #6680 from Walter Bright on github.com
28. ^D Language accepted for inclusion in GCC
29. ^'gdc project homepage'. Retrieved 14 October 2012.
30. ^'LLVM D compiler project on GitHub'. Retrieved 19 August 2016.
31. ^'BuildInstructionsPhobosDruntimeTrunk – ldc – D Programming Language – Trac'. Retrieved 11 August 2015.
32. ^'D .NET project on CodePlex'. Retrieved 3 July 2010.
33. ^Jonathan Allen (15 May 2009). 'Source for the D.NET Compiler is Now Available'. InfoQ. Retrieved 6 July 2010.
34. ^'DConf 2014: SDC, a D Compiler as a Library by Amaury Sechet'. Retrieved 8 January 2014.
35. ^'deadalnix/SDC'. Retrieved 8 January 2014.
36. ^'Wiki4D: EditorSupport/ZeusForWindows'. Retrieved 11 August 2015.
37. ^'Wiki4D: Editor Support'. Retrieved 3 July 2010.
38. ^'Google Project Hosting'. Retrieved 11 August 2015.
39. ^'descent'. Retrieved 11 August 2015.
40. ^'Visual D'. Retrieved 11 August 2015.
41. ^'dlang-vscode'. Retrieved 21 December 2016.
42. ^'code-d'. Retrieved 21 December 2016.
43. ^'Michel Fortin – D for Xcode'. Retrieved 11 August 2015.
44. ^'Mono-D – D Support for MonoDevelop'. Retrieved 11 August 2015.
45. ^'Dav1dde/lumen'. GitHub. Retrieved 11 August 2015.
46. ^'BBasile/Coedit'. GitHub. Retrieved 7 February 2017.
47. ^'poseidon'. Retrieved 11 August 2015.
48. ^'Mono-D – D Support for MonoDevelop'. Retrieved 11 August 2015.
49. ^'Entice Designer – Dprogramming.com – The D programming language'. Retrieved 11 August 2015.
50. ^'Under the Hood: warp, a fast C and C++ preprocessor'. Retrieved 4 January 2018.
51. ^'Faster Command Line Tools in D'. Retrieved 4 January 2018.
52. ^'Introducing Vectorflow'. Retrieved 4 January 2018.
53. ^'Quantum Break: AAA Gaming With Some D Code'. Retrieved 4 January 2018.
54. ^'Higgs JavaScript Virtual Machine'. Retrieved 4 January 2018.
55. ^'A D implementation of the ECMA 262 (Javascript) programming language'. Retrieved 4 January 2018.
56. ^'Project Highlight: The PowerNex Kernel'. Retrieved 4 January 2018.
57. ^'DCompute: Running D on the GPU'. Retrieved 4 January 2018.
58. ^'vibe.d - a high-performance asynchronous I/O, concurrency and web application toolkit written in D'. Retrieved 4 January 2018.
59. ^'Project Highlight: Diamond MVC Framework'. Retrieved 4 January 2018.
60. ^'Numeric age for D: Mir GLAS is faster than OpenBLAS and Eigen'. Retrieved 4 January 2018.
61. ^'On Tilix and D: An Interview with Gerald Nunn'. Retrieved 4 January 2018.
62. ^'Project Highlight: DlangUI'. Retrieved 4 January 2018.
63. ^'Project Highlight: Funkwerk'. Retrieved 4 January 2018.

Further reading[edit]

• Alexandrescu, Andrei (4 January 2010). The D Programming Language (1 ed.). Addison-Wesley Professional. ISBN978-0-321-63536-5.
• Alexandrescu, Andrei (15 June 2009). 'The Case for D'. Dr. Dobb's Journal.
• Bright, Walter (8 April 2014). 'How I Came to Write D'. Dr. Dobb's Journal.
• Çehreli, Ali (1 February 2012). 'Programming in D'. (distributed under CC-BY-NC-SA license). This book teaches programming to novices, but covers many advanced D topics as well.
• Metz, Cade (7 July 2014). 'The Next Big Programming Language You've Never Heard Of'. Wired.
• Ruppe, Adam (May 2014). D Cookbook (1 ed.). PACKT Publishing. ISBN978-1-783-28721-5.

External links[edit]

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• Official website
• Dlang on GitHub

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