You can take D as easy bridge to learn C++, or you can take D as modern programming language and replaces the ancient Pascal or even C.

MetaClass

“Class References” in Delphi/Pascal

SuperClass = class
    x: integer;
    constructor Create(value: integer)
    begin
      x := value;
    end;
end;

SubClass1 = class(SuperClass)
end;

SubClass2 = class(SuperClass)
end;

MyMetaClass = class of SuperClass;

//Assigning MetaClass of subclass, 
//compiler only accept classes that derived from SuperClass

var
   MC: MyMetaClass;

//Assigning
   MC = SubClass1;

//Creating object

   MyObj = MC.Create(10);

You can use classinfo, but is not a really like metaclass in Pascal but

it help you porting your projects

class SuperClass{
    int x;
    this(int value){
        x = value;
    }
}

class SubClass1: {
    this(){
    }
}

class SubClass2: {
    this(){
    }
}

Classinfo metaclass = SubClass.classinfo;

//Creating object

myObj = metaclass.create();

Disadvantage

You must have a default constructor to create it “this”, if no, myObj

will be null, and object not created

You can not use constructor with parameter like

    myObj = metaclass.create(10);

here you can assign to “mc” any class, not like Pascal that check if it

derived from class defined

Sets

You can use Associative Arrays (AA) of your enum.

enum MyEnum (A, B, C)

bool[MyEnum] mySet;

or you can make alias for it

bool[MyEnum] MySet;

MySet mySet;

mySet = [A: true, B: true];
//or
mySet[b] = true;

//Notice "in" operator in D meant the key is exists, not meant exists and equal to true
if (b in mySet){
}

Encapsulation

Private, Protected, Public

class MyClass{
private:
    ...
protected:
    ...
public:
    ...
}

Override

Not like Pascal, Every method is virtual until you mark it as final.

Strings

Index

String index started from 0
you can use length to get size

int i = s.length;

concat

s = "Hello ";
s = s ~ "World";

Pos

import std.string;

p = s.indexOf(".");

Copy

You can use slicing, because string is array of char

t = Copy(s, 1, 5);

In D

//Like this
t = s[0..5];
t = s[0..$]; //to the last of string

Notice that if you make range from x to same value it will return slice of empty string

t = s[2..2]; //Return empty string in t
t = s[2..3]; //Return one char index by 2

Generics

You can use the powerfull templates, this example make it clear to understand

type
  generic TList<T> = class
    procedure Add(Value: T);
  end;
...

Type  
  TIntegerList = specialize TList<Integer>;
  TStringList = specialize TList<string>;  

In D language

class List(T){
  void add(T t){
    //adding t
  }
}

class StringList: List!string{
}

IFDEF

debug, release, version(windows)

debug{
    ...
}

release{
    ...
}

debug writeln("Hello debug world");

version(windows){
//only for windows platform
}

You can define it also like this example

import std.stdio;

debug(everything)
{
    debug = level1;
    debug = level2;
    version = beta;
}

void main()
{
    debug(level1) writeln("level1...");
    debug(level2) writeln("level2...");
    version(beta) writeln("it is beta version");
}

And you can use “static if” to check condition at compile time, and stop the compilation useing “static assert”

struct MyType(T)
{
    static if (is (T == float)) {
        static assert(false, "float type is not supported");
    }
}

ref:http://ddili.org/ders/d.en/cond_comp.html

Helper

You dont need add help of class, just add global functions with paramter type of your class as first parameter.

class MyClass{
}

void doSomething(MyClass obj, int x){
}

Usage:

MyClass obj = new MyClass;

obj.doSomething(10);

Note: You can not access private or protected members on MyClass.

Functions

String Repeat:

    replicate(s, count);