New Delphi language features since Delphi 7

By: Nick Hodges

Abstract: See many of the major new language features in Delphi released after the Delphi 7 version

Language and Compiler Features Since Delphi 7

Inlining Routines can now be marked with the inline directive.  This tells the compiler that, instead of actually calling the routine, it should emit code that includes the routine at the call site.
Operator Overloading

Delphi allows certain functions, or operators, to be overloaded within record declarations



TMyClass = class
    class operator Add(a, b: TMyClass): TMyClass; // Addition of two operands of type TMyClass
    class operator Subtract(a, b: TMyClass): TMyclass; // Subtraction of type TMyClass
    class operator Implicit(a: Integer): TMyClass; // Implicit conversion of an Integer to type TMyClass
    class operator Implicit(a: TMyClass): Integer; // Implicit conversion of TMyClass to Integer
    class operator Explicit(a: Double): TMyClass; // Explicit conversion of a Double to TMyClass
end;

// Example implementation of Add class operator 
TMyClass.Add(a, b: TMyClass): TMyClass;
begin
  ...
end;

var
x, y: TMyClassbegin
  x := 12; // Implicit conversion from an Integer 
  y := x + x; // Calls TMyClass.Add(a, b: TMyClass): TMyClass 
  b := b + 100; // Calls TMyClass.Add(b, TMyClass.Implicit(100)) 
end;

Class Helpers

A class helper is a type that - when associated with another class - introduces additional method names and properties which may be used in the context of the associated class (or its descendants). Class helpers are a way to extend a class without using inheritance. A class helper simply introduces a wider scope for the compiler to use when resolving identifiers. When you declare a class helper, you state the helper name, and the name of the class you are going to extend with the helper. You can use the class helper any place where you can legally use the extended class. The compiler's resolution scope then becomes the original class, plus the class helper. Class helpers provide a way to extend a class, but they should not be viewed as a design tool to be used when developing new code. They should be used solely for their intended purpose, which is language and platform RTL binding.


type
  TMyClass = class

    procedure MyProc;
	function  MyFunc: Integer;
  end;

   ...

   procedure TMyClass.MyProc;
   var
	 X: Integer;
   begin
	  X := MyFunc;
   end;

   function TMyClass.MyFunc: Integer;
   begin
	   ...
   end;

...

type
   TMyClassHelper = class helper for TMyClass
	 procedure HelloWorld;
	 function MyFunc: Integer;
   end;

   ...

   procedure TMyClassHelper.HelloWorld;
   begin
	 WriteLn(Self.ClassName); // Self refers to TMyClass type, not TMyClassHelper

   end;

   function TMyClassHelper.MyFunc: Integer;
   begin
	 ...
   end;
...

var
  X: TMyClass;
begin
  X := TMyClass.Create;
  X.MyProc;    // Calls TMyClass.MyProc
  X.HelloWorld; // Calls TMyClassHelper.HelloWorld
  X.MyFunc; // Calls TMyClassHelper.MyFunc

end;
strict private The private keyword actually creates a " friendship" relationship between classes in the same unit.  The strict private declaration creates a true private field, not viewable by any other class, not even classes in the same unit.
strict protected Similar to the strict private declaration, strict protectedcreates a true protected member, visible only to the declaring class and its descendents.
Records with Methods

In addition to fields, records now may have properties and methods (including constructors), class properties, class methods, class fields, and nested types. 


type
  TMyRecord = record
    type
      TInnerColorType = Integer;
    var
      Red: Integer;
    class var
      Blue: Integer;
    procedure printRed();
    constructor Create(val: Integer);
    property RedProperty: TInnerColorType read Red write Red;
    class property BlueProp: TInnerColorType read Blue write Blue;
  end;

constructor TMyRecord.Create(val: Integer);
begin
  Red := val;
end;

procedure TMyRecord.printRed;
begin
  writeln('Red: ', Red);
end;
class abstract

Classes, and not just methods, can be declared as abstract.


type
  TAbstractClass = class abstract
    procedure SomeProcedure;
end;
class sealed Classes marked as sealed cannot be inherited from.

type
  TAbstractClass = class sealed
    procedure SomeProcedure;
end;
class const Classes can now have class constants -- a constant value associated with the class itself and not an instance of the class.

type
  TClassWithConstant = class
    public 
      const SomeConst = 'This is a class constant';
  end;
			

procedure TForm1.FormCreate(Sender: TObject);
begin
  ShowMessage(TClassWithConstant.SomeConst);
end;
class type A class can now contain a type declaration that is usable only within that class.


type
  TClassWithClassType = class
  private
	type
	  TRecordWithinAClass = record
	  SomeField: string;
	end;
  public

	    class var
	  RecordWithinAClass: TRecordWithinAClass;
  end;
  ...
procedure TForm1.FormCreate(Sender: TObject);
begin
  TClassWithClassType.RecordWithinAClass.SomeField := 'This is a field of a class type declaration';
  ShowMessage(TClassWithClassType.RecordWithinAClass.SomeField);
end;

class var A class can also have a class variable, applicable only to the class and not an instance of the class. See "class type" for an example.
class property A class can have a class property, which is a property that applies only to the class reference and not to an instance of a class.  The accessors for the class property must be either class methods or class variables. See the example in "static class methods" below.
nested classes Type declarations can be nested within class declarations. They present a way to keep conceptually related types together, and to avoid name collisions.

type
  TOuterClass = class
  strict private
	MyField: Integer;
  public
	type
      TInnerClass = class
	  public
        MyInnerField: Integer;
		procedure InnerProc;
      end;
      procedure OuterProc;
  end;

procedure TOuterClass.TInnerClass.InnerProc;
begin
  ...
end;
final methods A virtual method that you override can now be marked final, preventing derived classes from overriding that method.

TAbstractClass = classabstract
  public
    procedure Bar; virtual;
  end;

  TSealedClass = classsealed(TAbstractClass)
  public
    procedure Bar; override;
  end;

  TFinalMethodClass = class(TAbstractClass)
  public
    procedure Bar; override; final;
  end;
sealed methods Classes marked as sealed cannot be descended from. See the example in 'final methods'.
static class methods Classes can have static class methods -- i.e. methods that can be called from a class type. Class static methods can be accessed without an object reference. Unlike ordinary class methods, class static methods have no Self parameter at all. They also cannot access any instance members. (They still have access to class fields, class properties, and class methods.) Also unlike class methods, class static methods cannot be declared virtual.

type
  TMyClass = class
    strict private
      class var
        FX: Integer;
    strict protected  

    // Note: accessors for class properties must be declared class static.

      class function GetX: Integer; static;
	  class procedure SetX(val: Integer); static;
    public
      class property X: Integer read GetX write SetX;
	  class procedure StatProc(s: String); static;
  end;

TMyClass.X := 17;
TMyClass.StatProc('Hello');
for-in loop Delphi 2007 for Win32 supports for-element-in-collection style iteration over containers. The following container iteration patterns are recognized by the compiler:

  for Element in ArrayExpr do Stmt;
  for Element in StringExpr do Stmt;
  for Element in SetExpr do Stmt;
  for Element in CollectionExpr do Stmt;

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