Editing D (programming language) (section)

===Interaction with other systems===
[[C (programming language)|C]]'s [[application binary interface|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 [[Language binding|bindings]] are available for many popular C libraries. Additionally, C's standard [[library (computer science)|library]] is part of standard D.

On Microsoft Windows, D can access [[Component 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 as [[Callback (computer programming)|callbacks]]. 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, [[union type|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 like [[Python (programming language)|Python]],<ref>{{cite web |title=PyD |website=[[GitHub]] |url=https://github.com/ariovistus/pyd |access-date=2020-05-07 |date=7 May 2020}}</ref> [[Lua (programming language)|Lua]]<ref>{{cite web |last1=Parker |first1=Mike |title=Package derelict-lua on DUB |url=https://code.dlang.org/packages/derelict-lua |website=DUB Package Registry |access-date=2020-05-07}}</ref><ref>{{cite web |last1=Parker |first1=Mike |title=Package bindbc-lua on DUB |url=https://code.dlang.org/packages/bindbc-lua |website=DUB Package Registry |access-date=2020-05-07}}</ref> and other languages, often using compile-time code generation and compile-time type reflection methods.

====Interaction with C++ code====

For D code marked as <code>extern(C++)</code>, the following features are specified:

* The name mangling conventions shall match those of C++ on the target.
* For function calls, the ABI shall be equivalent.
* The vtable shall be matched up to single inheritance (the only level supported by the D language specification).

C++ namespaces are used via the syntax <code>extern(C++, namespace)</code> where ''namespace'' is the name of the C++ namespace.

=====An example of C++ interoperation=====
'''The C++ side'''
<syntaxhighlight lang="C++">
import std;

class Base {
    public:
        virtual void print3i(int a, int b, int c) = 0;
};

class Derived : public Base {
    public:
        int field;
        Derived(int field): 
            field(field) {}

        void print3i(int a, int b, int c) {
            std::println("a = {}", a);
            std::println("b = {}", b);
            std::println("c = {}", c);
        }

        int mul(int factor);
};

int Derived::mul(int factor) {
    return field * factor;
}

Derived* createInstance(int i) {
    return new Derived(i);
}

void deleteInstance(Derived*& d) {
    delete d;
    d = 0;
}
</syntaxhighlight>

'''The D side'''
<syntaxhighlight lang="D">
extern(C++) {
    abstract class Base {
        void print3i(int a, int b, int c);
    }

    class Derived : Base {
        int field;
        @disable this();
        override void print3i(int a, int b, int c);
        final int mul(int factor);
    }

    Derived createInstance(int i);
    void deleteInstance(ref Derived d);
}

void main() {
    import std.stdio;

    auto d1 = createInstance(5);
    writeln(d1.field);
    writeln(d1.mul(4));

    Base b1 = d1;
    b1.print3i(1, 2, 3);

    deleteInstance(d1);
    assert(d1 is null);

    auto d2 = createInstance(42);
    writeln(d2.field);

    deleteInstance(d2);
    assert(d2 is null);
}
</syntaxhighlight>