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| D | |
|---|---|
 | |
| Paradigm | Multi-paradigm:functional,imperative,object-oriented |
| Designed by | Walter Bright,Andrei Alexandrescu (since 2007) |
| Developer | D Language Foundation |
| First appeared | 8 December 2001; 23 years ago (2001-12-08)[1] |
| Stable release | |
| Typing discipline | Inferred,static,strong |
| OS | FreeBSD,Linux,macOS,Windows |
| License | Boost[3][4][5] |
| Filename extensions | .d, .di, .dd[6][7] |
| Website | dlang |
| Majorimplementations | |
| DMD (reference implementation),GCC, GDC, LDC,SDC | |
| Influenced by | |
| BASIC,[8]C,C++,C#,Eiffel,[9]Java,Python,Ruby | |
| Influenced | |
| Genie, MiniD (since renamed Croc),Qore,Swift,[10]Vala,C++11,C++14,C++17,C++20,Go,C#, others | |
| |
D, also known asdlang, is amulti-paradigmsystemprogramming language created byWalter Bright atDigital Mars and released in 2001.Andrei Alexandrescu joined the design and development effort in 2007. Though it originated as a re-engineering ofC++, D is now a very different language. As it has developed, it has drawn inspiration from otherhigh-level programming languages. Notably, it has been influenced byJava,Python,Ruby,C#, andEiffel.
The D language reference describes it as follows:
D is a general-purpose systems programming language with a C-like syntax that compiles to native code. It is statically typed and supports both automatic (garbage collected) and manual memory management. D programs are structured as modules that can be compiled separately and linked with external libraries to create native libraries or executables.[11]
D is notsource-compatible with C and C++ source code in general. However, any code that is legal in both C/C++ and D should behave in the same way.
Like C++, D hasclosures,anonymous functions,compile-time function execution,design by contract, ranges, built-in container iteration concepts, andtype inference. D's declaration, statement and expressionsyntaxes also closely match those of C++.
Unlike C++, D also implementsgarbage collection,first classarrays (std::array in C++ are technically not first class),array slicing,nested functions andlazy evaluation. D uses Java-style single inheritance withinterfaces andmixins rather than C++-stylemultiple inheritance.
D is a systems programming language. Like C++, and unlike application languages such asJava andC#, D supportslow-level programming, includinginline assembler. Inline assembler allows programmers to enter machine-specificassembly code within standard D code. System programmers use this method to access the low-level features of theprocessor that are needed to run programs that interface directly with the underlyinghardware, such asoperating systems anddevice drivers. Low-level programming is also used to write higherperformance code than would be produced by acompiler.
D supportsfunction overloading andoperator overloading. Symbols (functions,variables,classes) can be declared in any order;forward declarations are not needed.
In D, text character strings are arrays of characters, and arrays in D are bounds-checked.[12] D hasfirst class types for complex and imaginary numbers.[13]
D supports five mainprogramming paradigms:
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, unlike C, D'sforeach loop construct allows looping over a collection. D also allowsnested functions, which are functions that are declared inside another function, and which may access the enclosing function'slocal variables.
importstd.stdio;voidmain(){intmultiplier=10;intscaled(intx){returnx*multiplier;}foreach(i;0..10){writefln("Hello, world %d! scaled = %d",i,scaled(i));}}
Object-oriented programming in D is based on a singleinheritance hierarchy, with all classes derived from class Object. D does not support multiple inheritance; instead, it uses Java-styleinterfaces, which are comparable to C++'s pure abstract classes, andmixins, which separate common functionality from the inheritance hierarchy. D also allows the defining of static and final (non-virtual) methods in interfaces.
Interfaces and inheritance in D supportcovariant types for return types of overridden methods.
D supports type forwarding, as well as optional customdynamic dispatch.
Classes (and interfaces) in D can containinvariants which are automatically checked before and after entry to public methods, in accordance with thedesign by contract methodology.
Many aspects of classes (and structs) can beintrospected automatically at compile time (a form ofreflective programming (reflection) usingtype traits) and at run time (RTTI /TypeInfo), to facilitate generic code or automatic code generation (usually using compile-time techniques).
D supportsfunctional programming features such asfunction literals,closures, recursively-immutable objects and the use ofhigher-order functions. There are two syntaxes for anonymous functions, including a multiple-statement form and a "shorthand" single-expression notation:[14]
intfunction(int)g;g=(x){returnx*x;};// longhandg=(x)=>x*x;// shorthand
There are two built-in types for function literals,function, which is simply a pointer to a stack-allocated function, anddelegate, which also includes a pointer to the relevantstack frame, the surrounding ‘environment’, which contains the current local variables. Type inference may be used with an anonymous function, in which case the compiler creates adelegate unless it can prove that an environment pointer is not necessary. Likewise, to implement a closure, the compiler places enclosed local variables on theheap 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 aspure andnothrow to a function's type, if it can prove that they apply.
Other functional features such ascurrying and common higher-order functions such asmap,filter, andreduce are available through the standard library modulesstd.functional andstd.algorithm.
importstd.stdio,std.algorithm,std.range;voidmain(){int[]a1=[0,1,2,3,4,5,6,7,8,9];int[]a2=[6,7,8,9];// must be immutable to allow access from inside a pure functionimmutablepivot=5;intmySum(inta,intb)purenothrow/* pure function */{if(b<=pivot)// ref to enclosing-scopereturna+b;elsereturna;}// passing a delegate (closure)autoresult=reduce!mySum(chain(a1,a2));writeln("Result: ",result);// Result: 15// passing a delegate literalresult=reduce!((a,b)=>(b<=pivot)?a+b:a)(chain(a1,a2));writeln("Result: ",result);// Result: 15}
Alternatively, the above function compositions can be expressed using Uniform function call syntax (UFCS) for more natural left-to-right reading:
autoresult=a1.chain(a2).reduce!mySum();writeln("Result: ",result);result=a1.chain(a2).reduce!((a,b)=>(b<=pivot)?a+b:a)();writeln("Result: ",result);
Parallel programming concepts are implemented in the library, and do not require extra support from the compiler. However the D type system and compiler ensure that data sharing can be detected and managed transparently.
importstd.stdio:writeln;importstd.range:iota;importstd.parallelism:parallel;voidmain(){foreach(i;iota(11).parallel){// The body of the foreach loop is executed in parallel for each iwriteln("processing ",i);}}
iota(11).parallel is equivalent tostd.parallelism.parallel(iota(11)) by using UFCS.
The same module also supportstaskPool which can be used for dynamic creation of parallel tasks, as well as map-filter-reduce and fold style operations on ranges (and arrays), which is useful when combined with functional operations.std.algorithm.map returns a lazily evaluated range rather than an array. This way, the elements are computed by each worker task in parallel automatically.
importstd.stdio:writeln;importstd.algorithm:map;importstd.range:iota;importstd.parallelism:taskPool;/* On Intel i7-3930X and gdc 9.3.0: * 5140ms using std.algorithm.reduce * 888ms using std.parallelism.taskPool.reduce * * On AMD Threadripper 2950X, and gdc 9.3.0: * 2864ms using std.algorithm.reduce * 95ms using std.parallelism.taskPool.reduce */voidmain(){autonums=iota(1.0,1_000_000_000.0);autox=taskPool.reduce!"a + b"(0.0,map!"1.0 / (a * a)"(nums));writeln("Sum: ",x);}
Concurrency is fully implemented in the library, and it does not require support from the compiler. Alternative implementations and methodologies of writing concurrent code are possible. The use of D typing system does help ensure memory safety.
importstd.stdio,std.concurrency,std.variant;voidfoo(){boolcont=true;while(cont){receive(// Delegates are used to match the message type.(intmsg)=>writeln("int received: ",msg),(Tidsender){cont=false;sender.send(-1);},(Variantv)=>writeln("huh?")// Variant matches any type);}}voidmain(){autotid=spawn(&foo);// spawn a new thread running foo()foreach(i;0..10)tid.send(i);// send some integerstid.send(1.0f);// send a floattid.send("hello");// send a stringtid.send(thisTid);// send a struct (Tid)receive((intx)=>writeln("Main thread received message: ",x));}
Metaprogramming is supported through 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 thefactorial of a number:
ulongfactorial(ulongn){if(n<2)return1;elsereturnn*factorial(n-1);}
Here, the use ofstatic 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:
templateFactorial(ulongn){staticif(n<2)enumFactorial=1;elseenumFactorial=n*Factorial!(n-1);}
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 compilerinfers their types from the right-hand sides of assignments:
enumfact_7=Factorial!(7);
This is an example ofcompile-time function execution (CTFE). Ordinary functions may be used in constant, compile-time expressions provided they meet certain criteria:
enumfact_9=factorial(9);
Thestd.string.format function performsprintf-like data formatting (also at compile-time, through CTFE), and the "msg"pragma displays the result at compile time:
importstd.string:format;pragma(msg,format("7! = %s",fact_7));pragma(msg,format("9! = %s",fact_9));
String mixins, combined with compile-time function execution, allow for the generation of D code using string operations at compile time. This can be used to parsedomain-specific languages, which will be compiled as part of the program:
importFooToD;// hypothetical module which contains a function that parses Foo source code// and returns equivalent D codevoidmain(){mixin(fooToD(import("example.foo")));}
Memory is usually managed withgarbage collection, but specific objects may be finalized immediately when they go out of scope. This is what the majority of programs and libraries written in D use.
In case more control over memory layout and better performance is needed, explicit memory management is possible using theoverloaded operatornew, by callingC'smalloc and free directly, or implementing custom allocator schemes (i.e. on stack with fallback, RAII style allocation, reference counting, shared reference counting). 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.[15] The manual gives many examples of how to implement different highly optimized memory management schemes for when garbage collection is inadequate in a program.[16]
In functions,struct instances are by default allocated on the stack, whileclass instances by default allocated on the heap (with only reference to the class instance being on the stack). However this can be changed for classes, for example using standard library templatestd.typecons.scoped, or by usingnew for structs and assigning to a pointer instead of a value-based variable.[17]
In functions, static arrays (of known size) are allocated on the stack. For dynamic arrays, one can use thecore.stdc.stdlib.alloca function (similar toalloca in C), to allocate memory on the stack. The returned pointer can be used (recast) into a (typed) dynamic array, by means of a slice (however resizing array, including appending must be avoided; and for obvious reasons they must not be returned from the function).[17]
Ascope keyword can be used both to annotate parts of code, but also variables and classes/structs, to indicate they should be destroyed (destructor called) immediately on scope exit. Whatever the memory is deallocated also depends on implementation and class-vs-struct differences.[18]
std.experimental.allocator contains a modular and composable allocator templates, to create custom high performance allocators for special use cases.[19]
SafeD[20]is the name given to the subset of D that can be guaranteed to bememory safe. 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. 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.[21]
Initially under the banners of DIP1000[22] and DIP25[23] (now part of the language specification[24]), D provides protections against certain ill-formed constructions involving the lifetimes of data.
The current mechanisms in place primarily deal with function parameters and stack memory however it is a stated ambition of the leadership of the programming language to provide a more thorough treatment of lifetimes within the D programming language[25] (influenced by ideas fromRust programming language).
Within @safe code, the lifetime of an assignment involving areference type is checked to ensure that the lifetime of the assignee is longer than that of the assigned.
For example:
@safevoidtest(){inttmp=0;// #1int*rad;// #2rad=&tmp;// If the order of the declarations of #1 and #2 is reversed, this fails.{intbad=45;// The lifetime of "bad" only extends to the scope in which it is defined.*rad=bad;// This is valid.rad=&bad;// The lifetime of rad is longer than bad, hence this is not valid.}}
When applied to function parameter which are either of pointer type or references, the keywordsreturn andscope constrain the lifetime and use of that parameter.
The language standard dictates the following behaviour:[26]
| Storage Class | Behaviour (and constraints to) of a parameter with the storage class |
|---|---|
| scope | References in the parameter cannot be escaped. Ignored for parameters with no references |
| return | Parameter may be returned (or, in case ofvoid functions: copied to the first parameter), but otherwise does not escape from the function. Such copies are required not to outlive the argument(s) they were derived from. Ignored for parameters with no references |
An annotated example is given below.
@safe:int*gp;voidthorin(scopeint*);voidgloin(int*);int*balin(returnscopeint*p,scopeint*q,int*r){gp=p;// Error, p escapes to global variable gp.gp=q;// Error, q escapes to global variable gp.gp=r;// OK.thorin(p);// OK, p does not escape thorin().thorin(q);// OK.thorin(r);// OK.gloin(p);// Error, p escapes gloin().gloin(q);// Error, q escapes gloin().gloin(r);// OK that r escapes gloin().returnp;// OK.returnq;// Error, cannot return 'scope' q.returnr;// OK.}
C'sapplication 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. Dbindings are available for many popular C libraries. Additionally, C's standardlibrary is part of standard D.
On Microsoft Windows, D can accessComponent Object Model (COM) code.
As long as memory management is properly taken care of, many other languages can be mixed with D in a single binary. For example, the GDC compiler allows to link and intermix C, C++, and other supported language codes such as Objective-C. D code (functions) can also be marked as using C, C++, Pascal ABIs, and thus be passed to the libraries written in these languages ascallbacks. Similarly data can be interchanged between the codes written in these languages in both ways. This usually restricts use to primitive types, pointers, some forms of arrays,unions, structs, and only some types of function pointers.
Because many other programming languages often provide the C API for writing extensions or running the interpreter of the languages, D can interface directly with these languages as well, using standard C bindings (with a thin D interface file). For example, there are bi-directional bindings for languages likePython,[27]Lua[28][29] and other languages, often using compile-time code generation and compile-time type reflection methods.
For D code marked asextern(C++), the following features are specified:
C++ namespaces are used via the syntaxextern(C++, namespace) wherenamespace is the name of the C++ namespace.
The C++ side
importstd;classBase{public:virtualvoidprint3i(inta,intb,intc)=0;};classDerived:publicBase{public:intfield;Derived(intfield):field(field){}voidprint3i(inta,intb,intc){std::println("a = {}",a);std::println("b = {}",b);std::println("c = {}",c);}intmul(intfactor);};intDerived::mul(intfactor){returnfield*factor;}Derived*createInstance(inti){returnnewDerived(i);}voiddeleteInstance(Derived*&d){deleted;d=0;}
The D side
extern(C++){abstractclassBase{voidprint3i(inta,intb,intc);}classDerived:Base{intfield;@disablethis();overridevoidprint3i(inta,intb,intc);finalintmul(intfactor);}DerivedcreateInstance(inti);voiddeleteInstance(refDerivedd);}voidmain(){importstd.stdio;autod1=createInstance(5);writeln(d1.field);writeln(d1.mul(4));Baseb1=d1;b1.print3i(1,2,3);deleteInstance(d1);assert(d1isnull);autod2=createInstance(42);writeln(d2.field);deleteInstance(d2);assert(d2isnull);}
The D programming language has an official subset known as "Better C".[30] This subset forbids access to D features requiring use of runtime libraries other than that of C.
Enabled via the compiler flags "-betterC" on DMD and LDC, and "-fno-druntime" on GDC,Better C may only call into D code compiled under the same flag (and linked code other than D) but code compiled without theBetter C option may call into code compiled with it: this will, however, lead to slightly different behaviours due to differences in how C and D handle asserts.
core.thread)core.syncWalter Bright started working on a new language in 1999. D was first released in December 2001[1] and reached version 1.0 in January 2007.[31] The first version of the language (D1) concentrated on the imperative, object oriented and metaprogramming paradigms,[32] similar to C++.
Some members of the D community dissatisfied with Phobos, D's officialruntime andstandard library, created an alternative runtime and standard library named Tango. The first public Tango announcement came within days of D 1.0's release.[33] 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.[34]
In June 2007, the first version of D2 was released.[35] The beginning of D2's development signaled D1's stabilization. The first version of the language has been placed in maintenance, only receiving corrections and implementation bugfixes. D2 introducedbreaking changes to the language, beginning with its first experimentalconst system. D2 later added numerous other language features, such asclosures,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.[36]
The release ofAndrei Alexandrescu's bookThe 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 toGitHub. This has led to a significant increase in contributions to the compiler, runtime and standard library.[37]
In December 2011, Andrei Alexandrescu announced that D1, the first version of the language, would be discontinued on 31 December 2012.[38] The final D1 release, D v1.076, was on 31 December 2012.[39]
Code for the official D compiler, theDigital Mars D compiler by Walter Bright, was originally released under a customlicense, qualifying assource available but not conforming to theOpen Source Definition.[40] In 2014, the compilerfront-end wasre-licensed asopen source under theBoost Software License.[3] This re-licensed code excluded the back-end, which had been partially developed atSymantec. On 7 April 2017, the whole compiler was made available under the Boost license after Symantec gave permission to re-license the back-end, too.[4][41][42][43] On 21 June 2017, the D Language was accepted for inclusion in GCC.[44]
Most current D implementationscompile directly intomachine code.
Production ready compilers:
Toy and proof-of-concept compilers:
Using above compilers and toolchains, it is possible to compile D programs to target many different architectures, includingIA-32,amd64,AArch64,PowerPC,MIPS64,DEC Alpha,Motorola m68k,SPARC,s390,WebAssembly. The primary supported operating systems areWindows andLinux, but various compilers also supportMac OS X,FreeBSD,NetBSD,AIX,Solaris/OpenSolaris andAndroid, either as a host or target, or both.WebAssembly target (supported via LDC and LLVM) can operate in any WebAssembly environment, like modern web browser (Google Chrome,Mozilla Firefox,Microsoft Edge,Apple Safari), or dedicated Wasm virtual machines.
Editors andintegrated development environments (IDEs) supportingsyntax highlighting and partialcode completion for the language includeSlickEdit,Emacs,vim,SciTE,Smultron, Zeus,[57] andGeany among others.[58]
Open source D IDEs forWindows exist, some written in D, such as Poseidon,[71] D-IDE,[72] and Entice Designer.[73]
D applications can be debugged using any C/C++ debugger, likeGNU Debugger (GDB) orWinDbg, although support for various D-specific language features is extremely limited. On Windows, D programs can be debugged usingDdbg, or Microsoft debugging tools (WinDBG and Visual Studio), after having converted the debug information usingcv2pdb. TheZeroBUGSArchived 23 December 2017 at theWayback Machine 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 owngraphical user interface (GUI).
DustMite is a tool for minimizing D source code, useful when finding compiler or tests issues.[74]
dub is a popular package and build manager for D applications and libraries, and is often integrated into IDE support.[75]
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Notable organisations that use the D programming language for projects includeFacebook,[76]eBay,[77] andNetflix.[78]
D has been successfully used forAAA games,[79] language interpreters, virtual machines,[80][81] anoperating systemkernel,[82]GPU programming,[83]web development,[84][85]numerical analysis,[86]GUI applications,[87][88] apassenger information system,[89] machine learning,[90] text processing, web and application servers and research.
The North Korean hacking groupLazarus exploited CVE-2021-44228, aka "Log4Shell," to deploy threemalware families written in DLang.[91]
The lack of agility in the development process and the difficulty of introducing changes to the D language are described in a blog post article[92] by a former contributor. The apparent frustration described there has led to theOpenD fork[93] on January 1, 2024.
This article incorporates text from thisfree content work. Licensed under BSL-1.0 (license statement/permission).
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