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March 05, 2002
I have a project to do on D in college.(www.itb.ie).
Can some of ye just reply a couple of flash things about D, things like why
would be used instead of existing languages, and why it was made ?

I can make it available when done, if anyone is interested(deadline is this
friday).




March 05, 2002
Re: quick


was meant to change that subject.



March 05, 2002
i only program in C in college, with limited c++ exposure, and i cant find the difference between C++ and D :(


March 05, 2002
"Brian Folan" <99541157@itb.ie> wrote in message news:a62kuq$2tgd$1@digitaldaemon.com...

> i only program in C in college, with limited c++ exposure, and i cant find the difference between C++ and D :(

I recommend you to read the "Overview" and "Converting C++ to D" sections of the D manual for detailed explanations, but here are the most important (IMO) features you should be aware of:

- Objects are never instantiated on stack. In C++, this is a common
  practice. In D, you always use operator new to create an object.
  Variables of type "object" are actually references to objects, and
  not objects themselves:

    /* C++ */
    class Foo { ... }
    Foo bar;    // bar is an instance of Foo
    Foo* baz;   // baz is a pointer to instance of Foo

    /* D */
    class Foo { ... }
    Foo bar;    // bar is a reference (strict pointer) to instance of Foo
    Foo* baz;   // baz is a pointer to reference to instance of Foo

- In C++, classes and structs are pretty much the same. In D, the "class"
  keyword declares what is called class in C++, and D "struct" has the
  abilities of C (not C++) structure.

- C++ program can be divided into parts by writing several .cpp files, and
  providing an interface header .h file for each; this mechanism relies
  on preprocessor to #include interface files. Namespaces are separately
  provided by the namespace statement. D divides programs into modules,
  each .d file is a separate module with its own namespace; you import
  modules with the import directive, and there is no need for separate
  interface files.

- C++ requires global types, constants, variables, functions to be declared
  before they are used, and introduces a special syntax to provide forward
  references. In D you can use function declared in your module from any
  point of that module:

    /* C++ */
    void bar();    // forward declaration needed
    void foo() { bar(); }
    void bar() { foo(); }

    /* D */
    void foo() { bar(); }    // bar() is already visible!
    void bar() { foo(); }

- In C++, class members are private by default. In D, they are public
  by default. Also, you cannot use the public/private/protected specifier
  when inheriting from base class - it's always public:

    /* C++ */
    class Foo: public Bar { ... }

    /* D */
    class Foo: Bar { ... }

- In C++, bodies of member functions can be defined outside class
definition,
  and it is the prefferd way. This is not possible (nor it is needed) in D:

    /* C++ */
    class Foo
    {
        void bar();
    }
    void Foo::bar() { ... }

    /* D */
    class Foo
    {
        void bar() { ... }
    }

- C++ has three distinct resolution operators: "." (direct member access), "->" (indirect member access), and "::" (static member access). C++ also uses "::" to access member of the base class, or namespace. These all are replaced by a single "." in D, and compiler determines the exact meaning depending on the context:

    /* C++ */
    struct Foo { int n; }
    Foo bar;
    Foo* baz;
    bar.n = 1; baz->n = 1;

    /* D */
    struct Foo { int n; }
    Foo bar;
    Foo* baz;
    bar.n = 1; baz.n = 1;

- Constructor/destructor semantics are different:

    /* C++ */
    class Foo
    {
        Foo()  { ... }     // constructor
        ~Foo() { ... }     // destructor
    }

    /* D */
    class Foo
    {
        this()  { ... }    // constructor
        ~this() { ... }    // destructor
    }

- To call methods of base class, you use the pseudo-variable "super":

    /* C++ */
    class Foo
    {
        public: void baz() { ... }
    }

    class Bar: public Foo
    {
        public: void baz() { Foo::baz(); /* call version of base class */ }
    }

    /* D */
    class Foo
    {
        void baz() { ... }
    }

    class Bar: Foo
    {
        void baz() { super.baz(); /* call version of base class */ }
    }

- In C++, you have to call constructor of the base class (or it is
  done for you implicitly) at the beginning of your constructor using
  a weird syntax. Also, you cannot call one constructor of your class
  from another in that class. In D, constructors are just functions,
  and are called as such:

    /* C++ */
    class Foo
    {
    public:
        Foo() { default_ctor(); }
        Foo(int n) { default_ctor(); ... }
    private:
        void default_ctor() { /* does what needs to be done in any case */ }
    }

    class Bar: public Foo
    {
        public: Bar(int n): Foo(n) { ... }
    }

    /* D */
    class Foo
    {
        this() { /* does what needs to be done in any case */ }
        this(int n) { this(); ... }
    }

    class Bar: Foo
    {
        this(int n) { super(n); ... }
    }

- D syntax for array and pointer declarations is a bit different from C++ one:

    /* C++ */
    int foo, bar[5];  // foo is int, bar is array of ints
    int* foo, bar;    // foo is pointer to int, bar is int

    /* D */
    int[5] foo, bar;  // both foo and bar are arrays of ints
    int* foo, bar;    // both foo and bar are pointers to int

- D types are a bit different from those of C++. Here's the equivalence
table
  for a typical Win32 C++ compiler:

    D         ->   32-bit C++

    char      ->   char
    byte      ->   signed char
    ubyte     ->   unsigned char
    short     ->   signed short
    ushort    ->   unsigned short
    int       ->   signed int, signed long
    uint      ->   unsigned int, unsigned long
    long      ->   N/A (64-bit signed int, signed long long in GCC)
    ulong     ->   N/A (64-bit unsigned int, unsigned long long in GCC)
    float     ->   float
    double    ->   double
    extended  ->   long double
    complex   ->   std::complex
    imaginary ->   N/A

- D provides built-in dynamic arrays, with functionality similar
  to the one provided by std::vector class from C++ STL; the syntax
  is much simpler, however:

    /* C++ */
    vector<int> foo;    // dynamic arrays of ints
    foo.push_back(1);   // append 1 to the end of the array
    foo[0] = 2;       // element access
    // iteration
    for (int i = 0; i < foo.size(); i++)
        foo[i] = 666;

    /* D++ */
    int[] foo;     // dynamic array of ints
    foo ~= 1;      // append 1 to the end of the arrat
    foo[0] = 2;  // element access
    // iteration
    for (int i = 0; i < foo.length; i++)
        foo[i] = 666;

- Strings are represented by dynamic arrays of chars, rather than
  by pointers to null-terminated char sequences or std::string
  C++ STL class:

    /* C++ */
    string foo, bar, baz;
    foo = "Hello, ";
    bar = "world!";
    baz = foo + bar;    // concatenate with +
    baz += "\n";        // append with +=

    /* D */
    char[] foo, bar, baz;
    foo = "Hello, ";
    bar = "world!";
    baz = foo ~ bar;    // concatenate with ~
    baz ~= "\n";        // append with ~=

- Everything is garbage-collected. That is, everything allocated
  by operator new, be it an object or a dynamic array, gets freed
  automatically, you don't have to use operator delete. This allows
  you to write code that is unsafe (and thus considered "bad") in
  C++, but perfectly legal in D:

    /* bad C++, but legal D */
    int* foo(int n)
    {
        int* result;
        result = new int[n];
        return result;
    }

    void main()
    {
        int* array = foo(5);
        ...
        return 0;    // forgot to delete array! OK in D, bad thing in C++
    }

Oh, damn, I've tired of typing. =) There are SO many differences...
I haven't mentioned array slicing, design by contract (the "Contracts"
section in the D reference is a MUST READ!), interfaces, type complex,
standard library, and many other things. Once again, the best idea
is to read the entire D reference document, everything's there...


March 05, 2002
Woah, it was a large one. I should probably have copyrighted it =) But now it's too late... so enjoy it for free =)


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