c++ - D 编程：组件边界处的接口

Question

C++ 严重依赖 C 风格来导出和导入函数（如果有的话，不是类/接口），因此失去了面向对象的风格，这在许多方面使导出的接口变得晦涩难懂。

D 编程语言可以用于导出面向对象风格的接口吗？我可以用 D 接口包装 C++（纯）类吗？有哪些可能的考虑因素？这种方法是否可行。

Answer 1

您可以在此处找到有关 D 的 C++ 互操作性范围的概述。

面向对象风格的互操作性是通过 D 的interface构造提供的：

C++ 端

#include<iostream>

class I // Our interface-by-convention
{
public:
    virtual void foo() = 0;

    void bar() // OK, non-virtual members do not affect binary compatibility
    {
        /* ... */
    }
};

class C : public I
{
private:
    int a;

public:
    C(int a) : a(a) {}

    void foo()
    {
        std::cout << a << std::endl;
    }
};

// This function will be used from the D side
I* createC(int a)
{
    return new C(a);
}

D面

extern(C++) interface I
{
    void foo();

    final void bar() // OK, non-virtual members do not affect binary compatibility
    {
        /+ ... +/
    }
}

// Link `createC` from the C++ side
extern(C++) I createC(int a);

void main()
{
    I i = createC(2);
    i.foo(); // Write '2' to stdout
}

D's extern(C++) on the interface I causes the interface layout to replicate the layout of a single-inheritance C++ class with virtual functions in the companion C++ compiler.

The same attribute on the function declaration createC causes the function to replicate the mangling and calling convention of an equivalent function in the companion C++ compiler.

Companion compiler pairs: DMD/DMC++, GDC/g++, LDC/Clang. It's often possible to interoperate with a non-companion compiler by sticking to virtual functions and the C ABI for direct function calls.

Note that the createC function returns I* in C++ and just I in D. This is because D interfaces and classes are implicitly reference types.

In more typical real-world use, the createC function is more likely to be extern(C) than extern(C++) (and then extern "C" on the C++ side), for greater interoperability between compilers, or more straight-forward runtime linking when using DLLs.

extern(C++) currently has some limitations; it's currently not possible to tell D which namespace an extern(C++) declaration is in, limiting D to only being able to link to C++ symbols in the global namespace.