Object Pascal

Object Pascal

Paradigm	Imperative, Structured, Object-oriented, Functional (Delphi dialect only), Component-based, Event-driven, Generic
Designed by	Initially Apple Computer with input from Niklaus Wirth, and then by Borland International, led by Anders Hejlsberg
First appeared	1986 (1986)
Typing discipline	static and dynamic (dynamic typing through Variants, array of const and RTTI), strong, safe
Filename extensions	.p, .pp, .pas
Major implementations
Delphi (x86, ARM), Free Pascal (x86, x86-64, PowerPC, ppc64, SPARC, MIPS and ARM), Oxygene (CLI, Java, Native Cocoa), Smart Mobile Studio (JavaScript)
Dialects
Apple, Turbo Pascal, Free Pascal (using objfpc or delphi mode), Delphi, Delphi.NET, Delphi Web Script, Oxygene
Influenced by
Pascal, Simula, Smalltalk
Influenced
C#, Genie, Java, Nim

Object Pascal refers to a branch of object-oriented derivatives of Pascal, mostly known as the primary programming language of Embarcadero Delphi.

Early history at Apple

Object Pascal is an extension of the Pascal language that was developed at Apple Computer by a team led by Larry Tesler in consultation with Niklaus Wirth, the inventor of Pascal. It is descended from an earlier object-oriented version of Pascal called Clascal, which was available on the Lisa computer.

Object Pascal was needed in order to support MacApp, an expandable Macintosh application framework that would now be called a class library. Object Pascal extensions and MacApp itself were developed by Barry Haynes, Ken Doyle, and Larry Rosenstein, and were tested by Dan Allen. Larry Tesler oversaw the project, which began very early in 1985 and became a product in 1986.

An Object Pascal extension was also implemented in the Think Pascal IDE. The IDE includes the compiler and an editor with Syntax highlighting and checking, a powerful debugger and a class library. Many developers preferred Think Pascal over Apple's implementation of Object Pascal because Think Pascal offered a tight integration of its tools. The development stopped after the 4.01 version because the company was bought by Symantec. The developers then left the project.

Apple dropped support for Object Pascal when they moved from Motorola 68K chips to IBM's PowerPC architecture in 1994. MacApp 3.0, for this platform, was re-written in C++.

Borland and CodeGear years

In 1986, Borland introduced similar extensions, also called Object Pascal, to the Turbo Pascal product for the Macintosh, and in 1989 for Turbo Pascal 5.5 for DOS. When Borland refocused from DOS to Windows in 1994, they created a successor to Turbo Pascal, called Delphi and introduced a new set of extensions to create what is now known as the Delphi language.

The development of Delphi started in 1993 and Delphi 1.0 was officially released in the United States on 14 February 1995. While code using the Turbo Pascal object model could still be compiled, Delphi featured a new syntax using the keyword class in preference to object, the Create constructor and a virtual Destroy destructor (and negating having to call the New and Dispose procedures), properties, method pointers, and some other things. These were inspired by the ISO working draft for object-oriented extensions, but many of the differences from Turbo Pascal's dialect (such as the draft's requirement that all methods be virtual) were ignored.

The Delphi language has continued to evolve over the years to support constructs such as dynamic arrays, generics and anonymous methods.

Versions

• Borland used the name Object Pascal for the programming language in the first versions of Delphi, but later renamed it to the Delphi programming language. However, compilers that claim to be compatible with Object Pascal are often trying to be compatible with Delphi source code. Because Delphi is trademarked, compatible compilers continued using the name Object Pascal.
• Embarcadero Technologies, which purchased Delphi in 2008, sells the Delphi IDE that compiles the Delphi dialect of Object Pascal to Windows and macOS, iOS, Android and Web.
• .NET support existed from Delphi 8 through Delphi 2005, Delphi 2006 and Delphi 2007, which now has been replaced by another language, Oxygene (see below), which is not fully backward-compatible.
• The Oxygene programming language developed by RemObjects Software targets the Common Language Infrastructure, the Java (software platform) Runtime Environment and Apple's Cocoa frameworks for iOS and macOS.
• The open source Free Pascal project allows the language to be compiled for a wide range of operating systems—including Linux (32-bit and 64-bit), FreeBSD, Classic Mac OS/macOS, Solaris, Win32, Win64 and Windows CE—as well as for several different hardware architectures. The first version of Free Pascal for the iPhone SDK 2.x was announced on January 17, 2009. Now there is support for the ARM ISA also.
• The Smart Pascal programming language targets JavaScript/ECMAScript and is used in Smart Mobile Studio, written by Jon Lennart Aasenden and published by Optimale Systemer (2012). The language greatly simplifies HTML5 development through OOP and RAD (rapid application development) approaches. Smart Pascal integrates tightly with established technologies such as node.js, Embarcadero DataSnap and Remobjects SDK to deliver high-performance client/server web applications. The language allows for easy creation of visual components and re-usable libraries. The Smart Pascal dialect stems from the DWScript language- extended to better integrate with the JavaScript environment and libraries, such as "asm" sections which are plain JavaScript but have access to Pascal symbols, or "external" classes which map directly to prototypal JavaScript classes. Smart Pascal introduces true inheritance, classes, partial classes, interfaces, a virtual method table and many other advanced constructs which are not a part of JavaScript by default.
• MIDletPascal is aimed at the Java byte-code platform.
• The Morfik Pascal programming language developed by Morfik targets Ajax-enabled Web applications. The Morfik compiler is incorporated into the company's AppsBuilder IDE and allows Object Pascal code to be used in implementing code that will execute both in the browser and on the server. It uses the Free Pascal compiler to generate native binaries from Object Pascal.
• The open source GNU Pascal compiler is available as a front-end to the GNU compiler collection, which implements the ISO 7185 Pascal standard, and "most" of the ISO 10206 Extended Pascal standard.
• Also, a free compiler, Turbo51, is available for producing code for Intel 8051 chips.
• WDSibyl is an open source Delphi-like IDE and compiler available for Microsoft Windows and OS/2, and is a commercial Borland Pascal compatible environment released by a company called Speedsoft that was later developed into a Delphi like RAD environment called Sybil and then open sourced under the GPL when that company closed down. Wolfgang Draxler (WD) now maintains the software. (The compiler used seems to be located in a DLL and is not open-source).

Compilers

Object Pascal compilers are available for a wide range of operating systems and architectures.

• Embarcadero Delphi (formerly CodeGear Delphi and Borland Delphi) is probably the best known compiler. It is the successor of the highly successful Borland Pascal and Turbo Pascal product line. It targets Win16 (Delphi 1), Win32 (Delphi 2 and later), Windows 64-bit (Delphi XE2 and later), the .NET 1.x, 2.0 (Delphi 8, Delphi 2005–Delphi 2007) and macOS (Delphi XE2 and later), iOS (Delphi XE2 and later, generating native binaries in XE4 and later), Android (Delphi XE5 and later, generating native binaries in XE5 and later). Support for .NET finally became a separate product known as Oxygene (see below).
• Free Pascal Compiler (FPC) is an open-source Object Pascal compiler that supports many Pascal dialects, including those of Turbo Pascal 7 and Delphi, among others. Currently, FPC can generate code for x86, x86-64, PowerPC, SPARC, and ARM processors, and for various operating systems, including Microsoft Windows, Linux, FreeBSD, Classic Mac OS, and macOS (with an Xcode integration kit). Several separate projects exist to facilitate rapid application development with FPC, the most prominent one being the Lazarus IDE.
• GNU Pascal (A separately distributed part of the GNU Compiler Collection) While not formally aimed at the Delphi dialect of Pascal, it does contain a Borland Pascal compatibility mode, and is very slowly incorporating a few Delphi language features. It is unsuitable for recompiling large bodies of Delphi code directly, but is noteworthy as having prolific support for operating systems and hardware architectures.
• Oxygene (formerly known as Chrome) is an Object Pascal compiler from RemObjects Software that integrates into Microsoft Visual Studio. It is also available as free command-line compiler that runs native on CLI. It is three compilers in one, each targeting a different platform: Echoes for .NET/Mono/WinRT/Windows Phone 8, Cooper for Java & Android and Nougat for iOS & macOS.
• MIDletPascal is a mobile application development tool that generates Java ME bytecode.
• PocketStudio is a Pascal-based IDE for Palm OS.
• Smart Mobile Studio is a compiler that transforms Pascal source code to JavaScript (Source-to-source compiler)

Legacy products

• Borland Kylix was a Linux variant of Delphi which only targets Intel 32-bit Linux using the Qt library. It does not work out of the box with most modern Linux distributions.
• Virtual Pascal was a free 32-bit Turbo Pascal- and Delphi-compatible compiler aimed mainly at OS/2 and Microsoft Windows, although it also developed a DOS+ Extender and an experimental Linux cross-compiler. The compiler's development stopped at about the level of Delphi 2. In 2007, with its official website ceasing to operate, Virtual Pascal was discontinued from being further developed.

Interpreters

Main article: Pascal Script

Pascal Script (formerly known as InnerFuse) and DWScript (Delphi Web Script) are open-source Object Pascal interpreters/scripting engines written in Delphi. They support subsets of Object Pascal. DWScript can also compile Object Pascal code into JavaScript code (Smart Pascal), and supports just-in-time compilation.

Sample "Hello World" programs

Apple's Object Pascal

program ObjectPascalExample;

   type
      THelloWorld = object
         procedure Put;
      end;

   var
      HelloWorld: THelloWorld;

   procedure THelloWorld.Put;
   begin
      ShowMessage('Hello, World!');
   end;

begin
   New(HelloWorld);
   HelloWorld.Put;
   Dispose(HelloWorld);
end.

Turbo Pascal's Object Pascal

Still supported in Delphi and Free Pascal. FPC also packages its own substitutes for the libraries/units. Delphi doesn't. The Free Pascal 1.0 series and the FPC textmode IDE are the largest open codebases in this dialect. Free Pascal 2.0 was rewritten in a more Delphi-like dialect, and the textmode IDE and related frameworks (Free Vision) are the only parts in the TP version of Object Pascal.

Stack based allocation

program ObjectPascalExample;

   type
      THelloWorld = object
         procedure Put;
      end;

   procedure THelloWorld.Put;
   begin
      WriteLn('Hello, World!');
   end;

var
  HelloWorld: THelloWorld; { allocated on the stack and can be used without explicit allocation. }
begin
   HelloWorld.Put;
end.

Heap based allocation

program ObjectPascalExample;

   type
      PHelloWorld = ^THelloWorld;
      THelloWorld = object
         procedure Put;
      end;

   procedure THelloWorld.Put;
   begin
      WriteLn('Hello, World!');
   end;

var
  HelloWorld: PHelloWorld; { this is a typed pointer to a THelloWorld }

begin
   New(HelloWorld);
   HelloWorld^.Put;
   Dispose(HelloWorld);
end.

Another example:

program ObjectPascalExample;

   type
      PHelloWorld = ^THelloWorld;
      THelloWorld = object
         procedure Put;
      end;

   procedure THelloWorld.Put;
   begin
      WriteLn('Hello, World!');
   end;

var
  HelloWorld: PHelloWorld; { this is a typed pointer to a THelloWorld }
  HelloWorld2: ^THelloWorld; { this is a direct variable to a pointer of the THelloWorld type. 
                               This variable is type incompatible with PHelloWorld. } 
  HelloWorld3: ^THelloWorld; { the compiler sees this as being type incompatible with HelloWorld2 *and* 
                               PHelloWorld. Using the pointer syntax is the only way to declare a type that is 
                               assignment compatible. }
  HelloWorld4: PHelloWorld; { this is type compatible with HelloWorld, but incompatible with the other two variables. }
begin
   { This works in a similar way as the code above... but it demonstrates the disadvantage of not 
     using a specific type. The type definition between two variables using the raw pointer 
     based notation would be seen as "different" by the compiler. }

   New(HelloWorld4);
   HelloWorld := HelloWorld4; { this is valid - the type assignment is valid }
   HelloWorld2 = HelloWorld; { this would be a compiler error }
   {disposes left out for brevity}

   New(HelloWorld3);
   HelloWorld := HelloWorld3; { this would be a compiler error }
   HelloWorld2 = HelloWorld3; { this would be a compiler error }
   {disposes left out for brevity}
end.

This is an important distinction to make, and could be seen as one of the key differences that led to the Delphi style of "hiding" the heap allocation and pointer notation from the programmer. Delphi removed the need for the additional Pointer type and pointer syntax, but retained the explicit construction mechanism.

Delphi and Free Pascal's Object Pascal

program ObjectPascalExample;

type
  THelloWorld = class
    procedure Put;
  end;

procedure THelloWorld.Put;
begin
  Writeln('Hello, World!');
end;

var
  HelloWorld: THelloWorld;               { this is an implicit pointer }

begin
  HelloWorld := THelloWorld.Create;      { constructor returns a pointer to an object of type THelloWorld }
  HelloWorld.Put;
  HelloWorld.Free;                       { this line deallocates the THelloWorld object pointed to by HelloWorld }
end.

Note that the object construct is still available in Delphi and Free Pascal.

Oxygene Object Pascal

namespace ObjectPascalExample;

   interface

   type
      ConsoleApp = class
         class method Main;
      end;

      THelloWorld = class
         method Put;
      end;

   implementation

   method THelloWorld.Put;
   begin
      Console.WriteLine('Hello, World!');
   end;

   class method ConsoleApp.Main;
   begin
      var HelloWorld := new THelloWorld;
      HelloWorld.Put;
   end;

end.

DWScript's Object Pascal (aka Smart Pascal)

type
   THelloWorld = class
      procedure Put;
      begin
         PrintLn('Hello, World!');
      end
   end;

var HelloWorld := THelloWorld.Create;

HelloWorld.Put;

Note that the method implementation can also be made in a distinct location as in other Object Pascal dialects.

Development

Many features have been introduced continuously to Object Pascal with extensions to Delphi and extensions to FreePascal. In reaction to criticism, Free Pascal has adopted generics with the same syntax as Delphi, provided Delphi compatibility mode is selected, and both Delphi (partially) and Free Pascal (more extensive) support operator overloading. Delphi has also introduced many other features since version 7 including generics. Whereas FreePascal tries to be compatible to Delphi in Delphi compatibility mode, it also traditionally introduced many new features to the language that are not always available in Delphi.

See also

• Borland Kylix
• Comparison of programming languages
• Embarcadero Delphi
• Free Pascal
• Turbo51

External links

• Delphi Basics, Resource of Delphi Project Source Codes.
• Introduction to Object Pascal, MacTech Vol 2 Issue 12 1985.
• Object Pascal reference guide for Free Pascal. "The aim is to list which Pascal constructs are supported, and to show where the Free Pascal implementation differs from the Turbo Pascal or Delphi implementations."
  • Object Pascal reference guide for Free Pascal, downloadable PDF
• Delphi-Help - первая помощь программисту на Delphi
• Major Differences Between the Syntax of C++ and Object Pascal
• Delphi Programming, Resource of Delphi Programming & Delphi Programming Forums.