Delphi and PHP Cross Reference Guide

Delphi creates native code Windows applications so you can create an EXE with no dependencies that will run on any Windows computer. If you add dependencies (reports, database libraries, DLLs, etc.) use a Windows installer to build an installation program.

D2007 and D2009 are bundled with InstallAware Express CodeGear Edition installer.

With PHP, you simply copy your files to a web server that is capable of running PHP pages.

CodeGear Delphi is the primary tool of choice for most developers but other Object Pascal language development tools do exist and some are quite good.

Many developers just use a text editor. There are many PHP editors available including phpDesigner, and Delphi for PHP.

Common source code file extensions include:

• .BDSPROJ - Project, Borland Developer Studio project file holds compiler options, etc. This is the file you open.
• .DCU - Delphi Compiled Unit file.
• .DFM - Delphi Win32 form file (a text resource file).
• .DPR - Delphi project file. Primary project "source" file.
• .PAS - Delphi unit source file.

Note: Delphi 2009 changed the project file to acommadatte new features. When you open a project file from a previous version, it will be upgraded. In addition to .bdsproj, D2009 also uses a .dproj project file.

 Delphi File Extensions

 Ref: http://delphi.wikia.com/wiki/Delphi_File_Extensions

.php is the default extension for PHP although some developers will change the default extension in an effort to add an additional security level. If your code is tied to a particular version of PHP then some developers at the major PHP version number to the extension as in .php3, .php4, .php5, etc. 

.phtml is also sometimes used especially for files that contain both HTML and Perl code.

Language Overview: Delphi programming language is a type-safe language consisting of hybrid traditional Pascal and OOP features. You code either in a traditional approach using functions, procedures, and global data, or you code using an OOP approach, or a mixture of both.

Target Platforms: Delphi for Win32 is most suitable for creating native code Win32 applications that run on Microsoft Windows.

PHP is a hybrid language with both traditional PHP and OOP features. PHP is widely-used general-purpose scripting language that is especially suited for web development and can be embedded into HTML. PHP has been used to create some amazing web content, particularly outstanding message boards.

Target Platforms: PHP is most suitable for creating websites targeting any browser (any web server with PHP installed).

Rave Reports comes closest to a Delphi standard now but historically there has been no real standard in Delphi development. Do-it-yourself developers sometimes like to use TPrinter for very simple reports. ReportSmith was bundled with the first few versions of Delphi.

Delphi has offered many embedded VCL component report options. Quick Reports has been a part of Delphi since Delphi 2.0 and has been the default report writer for many Delphi developers. Ace Reporter, ReportBuilder and Rave Reports are also very popular. During the time of Kylix, FastReports was popular because of it's cross-platform nature.

Crystal Reports is very common because of it's overall popularity as a stand-alone report writer that integrates well with many different tools.

 Delphi Report Tools Overview

No built-in report writer but because website development targets a client browser (a document interfaced GUI), a common solution is to simply output an HTML formatted page with black text and a white background (not much control but it does work for some situations).

Object Pascal is generally not case sensitive.

Syntax Example:   Variables and commands are not case sensitive. var FullName: String; begin fullname := 'Mike Prestwood'; ShowMessage(fullNAME); SHOWMESSAGE(FULLNAME); showmessage(fullname); end;

 Camel versus Pascal Casing

PHP is case sensitive with variable names but not with commands. Although commands are case incenstive, I prefer to use all lowercase because it's easy to type and that's what I see most PHP coders doing and I see it on PHP.Net.

echo "hello<br>";

ECHO "hello<br>";

Echo "hello<br>";

eCHo "hello<br>";

$fullname = "Mike Prestwood"; //These are two...

$FullName = "Wes Peterson";   //separate varialbes.

Object Pascal requires the semi-colon after the "declaration" part.

function DoSomething : integer;

var

  a, b : integer

begin

  a := 1;

  b := 2;

  result := a + b;

end;

In .PHP html pages, you embed PHP code between <?PHP and ?>.

For PHP, JavaScript, Java,and C++, I prefer to put the first { at the end of the first line of the code block as in the example above because I see morePHP codeformatted that way (and on PHP.Net).

PHP Alternative Syntax

Although I don't like to use it, PHP offers an alternative syntax for if, while, for, foreach, and switch. These code blocks are surrounded by statement ending keywords that all use End with camel caps such as endif, endwhile, endfor, endforeach,and endswitch.

<?PHP

$x = "Yes";

//Simple if

If ($x == "Yes")
  echo "hello world";

//If with a block of code.

If ($x == "Yes") {
  echo "Hello world";

  echo "I am a PHP coder!";

}

?>

Commenting Code
Delphi uses // for a single line comment and both {} and (**) for multiple line comments. Although you can nest different types of multiple line comments, it is recommended that you don't.

Compiler Directives - $
A special comment. Delphi compiler directives are in the form of {$DIRECTIVE}. Of interest for comments is using the $IFDEF compiler directive to remark out code.

//This is a single line comment.

 
{

Multiple line

comment.

}

 
(*
This too is a
multiple line comment.
*)

 
{$IFDEF TEMPOUT}
  //...code here
{$ENDIF}

 Delphi Comments (// or { ... } or (* ... *))  

Commenting Code
Use the multi-line to comment out large blocks of code and to write multiple line comments.

#This is a comment in PHP.

//This is too!
 

/*

This is a multi-line

comment.

*/

In Delphi, you define constants similar to how you define variables but use the Const keyword instead of the Var keyword. Declare global constants in a unit's interface section and unit constants (scope limited to unit) in the implementation section. Declare local constants above the begin..end block.

Const 

  kFeetToMeter: Double = 3.2808;

  kMeterToFeet: Double = .3048;

  kName: String = "Mike";

//Local constants:

procedure SomeProcedure;

const

  kPI: Double=3.1459;

begin

end;

 Delphi Constants (Const kPI: Double=3.1459;)  

In PHP, you declare constants using the define keyword:

define("CONST_NAME", "Value");

Constants in PHP are case sensitive. A common standard in PHP is to use all-uppercase letters, with underscores to separate words within the name.

define('FULL_NAME', 'Mike Prestwood');
define("AGE", 25);

echo "Your name is " . FULL_NAME . ".";
echo "You are " . AGE . ".";

 PHP Constants (define)

Object Pascal uses a semicolon ";" as an end of statement specifier and you can put multiple statements on a single line of code and put a single statement on two or more code lines if you wish.

Syntax Example:   WriteLn('Hello1'); WriteLn('Hello2'); WriteLn('Hello3'); //Same line works too: WriteLn('Hello4'); WriteLn('Hello5'); //Two or more lines works too: WriteLn ('Hello6');

String literals are single quoted (the apostrophe) as in 'Prestwood'. If you need to embed an apostrophe use two apostrophes in a row.

Floating point literals must start with an integer. For example, to specify a fractional floating point literal between 1 and -1, you preceed the decimal with a 0; otherwise, you will get a compiler error.

//x := .1 + .1;   //Does not work.

x := 0.1 + 0.1;   //Does work.

Syntax Example:   ShowMessage('Hello'); ShowMessage('Hello Mike''s website.');

 Ref: https://forums.codegear.com/thread.jspa?threadID=8909&tstart=60

In PHP you can use quotes, or apostrophes as in "Prestwood", and 'Prestwood' for string literals. Use a slash in front of a quote or apostrophe to embed same type as in \' and \".

To specify a floating point literal between 1 and -1, you can preceed the decimal with a 0 or not (both work). In other words, preceding and following decimals are allowed (both .1 and 0.1). Trailing decimals are also allowed (1, 1., and 1.0 are all equivalent and allowed).

echo "Mike's drums are over there.<br>";
echo 'Mike said, "hi!"<br>';

//Does PHP evaluate this simple

//floating point math correctly? No! 

If ((.1 + .1 + .1) == .3) {
 Echo "Correct";
} Else {
 Echo "Not correct";
}

 PHP Literals (quote or apostrophe)

The Delphi language is a strongly typed language so you have to specifically declare variables and frequently use commands such as IntToStr and StrToInt.

Declare global variables in the interface section of a unit, variables declared within the implementation section (but not within a method) have a scope limited to the unit. You declare local variables in a var block outside (above) your begin..end code block. You cannot declare variables in-line (inside begin..end).

You can initialize global and unit variables but you cannot initialize local variables.

Delphi offers many variable types. Some common variable types include String, WideString, PChar, Integer, Boolean, Single, Double, Pointer, and Variant.

Note: D2009 introduced a new UnicodeString type.

procedure SomeProcedure;

var
  Fullname: String;
  Age: Integer;

  X, Y, Z: Double;

  MyArray: array [1..100] of Char;

begin

end;

//You can initialize global variables.

var

  ClickCounter: Integer = 0;

 Delphi Variables (var x: Integer = 0;)  

PHP is a loosely typed language. No variable types in PHP. Declaring and using variables are a bit different than in other languages. In PHP, you identify and use a variable with a $ even within strings!

You assign by reference with & as in &$MyVar.

$fullname = 'Mike Prestwood';
$FullName = 'Wes Peterson';   //This is a different variable!
$Age = 38;
$Weight = 162.4;

 

echo "Your name is $fullname.
";
echo "You are $Age and weigh $Weight.
";

 PHP Variables ($x = 0;)

Delphi is a hybrid language so you can create either class methods (functions and procedures) or you can create global functions and procedures. When a function or procedure is part of a class, it is a class method.

[function/procedure] RoutineName : ReturnType;

As with C++, your custom routine must come before it's first usage or you have to prototype it in the Interface section.

Note: Contrast Delphi with Delphi Prism which is an OOP language (everything is within a class). Both Delphi and Delphi Prism are based on Object Pascal but implement OOP features differently and have some syntax differences too.

procedure SayHello(pName: String);
begin
  ShowMessage('Hello ' + pName);
end;

function Add(p1, p2 : Double): Double;
begin
  Result := p1 + p2;
end;

 Delphi Custom Routines (procedure, function)

PHP uses functions and loosely typed parameters. Function definitions can come before or after their usage so my preference when mixing PHP in with a mostly HTML page is to put the functions after the </html> tag.

function sayHello($pName) {
 echo "Hello " . $pName . "<br>";
}

function add($p1, $p2) {
 return $p1 + $p2;
}

 PHP Custom Function (function)

Many objects in Delphi have events you can use to trigger code. For example, when you add a form to your project you have access to the form events such as onCreate, onShow, onHide, onDockDrop, etc. In addition, Delphi offers module level events initialization and finalization sections.

In Delphi, you can inline assembler code using the asm keyword.

Delphi introduced developer defined function and procedure inlining with Delphi 2005. Use the inline keyword to tell the compiler to try to inline a routine (a compiler hint). Since Delphi will only try to inline the routine, make sure you test for speed because inlining a routine can lead to slower code under some circumstances.

Syntax Example:   function Add(a, b: Integer): Integer; inline; begin end;

Delphi supports both method and operator overloading.

For method overloading, you use the overload keyword (all versions of the routine must include the overload keyword). The compiler chooses the correct method first based on the number of parameters, then on the type so you can have two overloaded methods with the same number of parameters so long as at least one parameter is different.

Another form of method overloading is with the use of default parameters, a shortcut syntax, where you specify a default parameter value.

Delphi also supports operator overloading with some operators.

function Add(a, b: integer): Integer;  overload;
begin
  Result := a+b;
end;

function Add(const msg: String; a, b: integer): String; overload;
begin
  Result := msg + IntToStr(a+b);
end;

 Delphi Overloading (overload)

PHP

• Operator - No.
• Method -

 PHP Overloading

Object Pascal allows parameters of the same type to be listed together, separated by commas, and followed with a single data type (more params of different data types can follow, after a semi-colon).

Delphi also supports default parameters (a form of overloading).

By Reference or Value (and by constant): The default for parameters is by value. For by reference, add var in front of the parameter. Object Pascal also offers constant parameters where you add const in front of the parameter. A constant parameter is like a local constant or read-only parameter the compiler can optimize. You cannot assign a value to a constant parameter, nor can you pass one as a var parameter to another routine. (But when you pass an object reference as a constant parameter, you can still modify the object's properties.)

function Add(a, b: integer) : integer; 
begin
  Result := a + b;
end;
  
procedure ReplaceTime(var pDT: TDateTime; const pNewDT: TDateTime);
begin
end;

 Delphi Parameters (var, const)  

Within the implementation of a method, the identifier Self references the object in which the method is called. The Self variable is an implicit parameter for each object method. A method can use this variable to refer to its owning class.

ShowMessage('Self=' + Self.ClassName);

Delphi supports both static and dynamic arrays as well as single and multi dimensional arrays.

var
  MyArray: array[0..3] of string;
  i: Integer;
begin
  MyArray[0] := 'Mike';
  MyArray[1] := 'Lisa';
  MyArray[2] := 'Felicia';
  MyArray[3] := 'Nathan';

  for i := 0 to High(MyArray) do
    ShowMessage(MyArray[i]);
end;

 Delphi Array (x=Array[0..3] of string;)  

Object Pascal doesn't have a native associative array, but you can use a TStringList the same way. (Alternatively, search the Internet for TStringHash and THashedStringList classes for implementations of a true associative array).

var
  StateList : TStringList;
begin
  StateList := TStringList.Create; 

  StateList.CommaText := 'CA=California, FL=Florida';

  ShowMessage('FL is ' + StateList.Values['FL']);
end;

 Associative Arrays in Delphi/Object Pascal (Use TStringList)

Declare associative array with initial known values. You can also add to associative array. (You can just assign values without ever declaring it too!)

$prices = array( 'Tires'=>100, 'Spark Plugs'=>4 );
$prices['Oil'] = 10;

echo "Tires=" . $prices['Tires'] . "<br>";
echo "Oil=" . $prices['Oil'] . "<br>";

 PHP Associative Array

Although pointer data types in Delphi coding are less important and not required for most general coding, Delphi fully supports developer defined pointers. Use a carrot (^) to declare a pointer data type. Use the @ operator or Addr function to return the current address of a variable.

Delphi provides typed pointer types such as PChar and PExtended as well as a generic point to anything Pointer type.

Nil is a special pointer value that you can assign to any type of pointer. Nil never points to any valid memory and indicates an unassigned or empty pointer.

//Declare a pointer of type integer.

PCounter : ^Integer;

//Assign a value to the location of a pointer.

//Also known as dereferencing.

PCounter^ := 8;

//Assign address of A to B.

PointerB := @PointerA;  //or...PointerB := Addr(PointerA);

PHP supports references which allow you to refer to the value of a variable but PHP does not support true developer defined pointers. You cannot get and use the address of a variable.

However, you can still do inexpensive assignments by assigning by reference.

Use a try..except..end block to trap and process errors.

Delphi also offers a try...finally where code will execute in the finally section no matter what. It's common to put a try..except inside a try..finally.

var
  y : Double;
begin
  try
    y := 0;
    y := (1/y);
    ShowMessage(FloatToStr(y));
  except
    ShowMessage('You cannot divide by zero.');
  end;
end;

Notice in the more complete example that the semicolon for the begin..end block after end is not included. That tells the compiler something else is coming (the statement is not finished). Also note the semicolon is missing right before the final "else" statement.

Note: The following example uses floating point literals. In Delphi, to specify a fractional floating point literal between 1 and -1, you preceed the decimal with a 0; otherwise, you will get a compiler error (i.e. .1 + .1 does not work).

if (0.1 + 0.1 + 0.1) = 0.3 then
  ShowMessage('Correct')
else
  ShowMessage('Not correct');

//Complete example:
if x = true then
begin 

  ShowMessage('x is true');

end

Else If y = 'Mike' Then 

  ShowMessage('hello mike')

Else 

  ShowMessage('last option');

 Delphi If Statement (If..Else If..Else)

The PHP if statement consists of using if, elseif, and else.

$x = 8;

if ($x == 10) {
 echo "x is 10.";  
} elseif ($x < 10) {
 echo "x is less than 10.";
} else {
 echo "x must be greater than 10.";  
};

Delphi uses := for it's assignment operator.

var

  FullName: String;

  Age: Integer;

begin

  FullName := "Randy Spitz";
  Age := 38;

end

PHP uses = for it's assignment operator.

$fullname = "Randy Spitz";

$age = 38;

Common comparison operators:

//Does Delphi evaluate the math correctly? Yes!

//Refer to math.pas MaxSingle for more info.

if (0.1 + 0.1 + 0.1 = 0.3) then
  ShowMessage('correct')
else
  ShowMessage('not correct')

 Delphi Comparison Operators (=, <>)

Common comparison operators:

PHP 4 and above also offers === for indentical (equal plus same type) and !== for not identical (not equal or not same type).

//Does PHP evaluate the math correctly? No!

if (.1 + .1 + .1 == .3) {
  echo "correct";
}
else {
  echo "not correct";
}

Length() or SizeOf() will correctly identify an unassigned string variable or an empty string.

if length(s) = 0 then
  ShowMessage('empty string');

Delphi logical operators:

The Delphi compiler default is to short circuit multi argument boolean expressions when the result is known before the evaluation completes. To disable short circuiting, use the {$B+} compiler directive. To reset it back to the compiler default of short circuting, use the {$B-} compiler directive.

//Given expressions a, b, c, and d:

if Not (a and b) and (c or d) then

  //Do something.

 Delphi Logical Operators  

PHP logical operators:

#Given expressions a, b, c, and d:

if !((a && b) && (c || d)) {

  #Do something.

};

Use the + operator to concatenate two strings. Use IntToStr to convert an integer to a string and FloatToStr to convert a floating point number to a string.

var 

  FirstName : String; 

  LastName : String;

begin 

  FirstName := 'Mike'; 

  LastName := 'Prestwood';

  ShowMessage('Full name: ' + FirstName + ' ' + LastName);

  ShowMessage(FloatToStr(3.2));

end;

PHP uses a period (.) known as a dot to concatenate strings.

$fname = "Mike";
$lname = "Prestwood";

$fullname = $fname . $lname . "
";

echo "My name is " . "Mike.
";

 PHP String Concatenation (.)

An operation with only one operand (a single input). In Object Pascal, a unary operator has the highest precedence and always precedes its operand (for example, -B), except for the  ^ pointer operator, which follows its operand (for example, P^). In addition to the obvious +, -, and Not operators, Delphi also offers:

The TYPE operator is also a unary operator and is valuated at compile time. The TYPE operator returns the size in bytes of the operand,

A unary operator operates on only one value.

PHP Examples:

• ! negation operator
• ++ increment operator
• -- decrement operator

 PHP Unary Operators

In Delphi programming language (Object Pascal), all classes ultimately inherit from the base class TObject.

//Specify both namespace and class:

TCyborg = class(System.TObject)
end;

//Use shortcut alias:

TCyborg = class(TObject)
end;

//None, default is System.TObject

TCyborg = class
end;

 Delphi Base Class (TObject)  

Declare your class in the Interface section. Then implement the class in the Implementation section. To create an object instance, call the class constructor (usually named Create). Since Delphi does not have a garbage collector, you have to also free the object usually with either Free or FreeAndNil.

//Interface section:

TCyborg = class(TObject)
public
 procedure IntroduceYourself;
end;

//Implementation section;

procedure TCyborg.IntroduceYourself;
begin
 ShowMessage('Hi, I do not have a name yet.');
end;

//Some event like a button click:

var
  T1: TCyborg;
begin
  T1 := T1.Create;
  T1.IntroduceYourself;

  FreeAndNil(T1);      //Be sure to clean up!
end;

 Delphi Class..Object (class..end..Create)

In Delphi, you use the class keyword followed by the parent class in parens. If you leave out the parent class, your class inherits from TObject.

TAndroid = class

end;

T-600 = class(TAndroid)

end;

 Delphi Inheritance (=class(ParentClass))  

In Delphi, member events are essentially properties of the type method pointer.

In Delphi, it is common to start all member fields with "F" as in FName and FAge. You can initialize the value of member fields too.

Delphi member fields do not support static data. The workaround is to use the hybrid nature of Delphi and use a unit variable (a variable declared in the implementation section of a unit) and then access the unit variable with a member property.

Delphi doesn't support setting a member field to read-only. However, you can accomplish the task with a strict private member field and a read-only property.

TCyborg = class(TObject)
private
  FSerialNumber: String='A100';
public
  FCyborgName: String;
  FCyborgAge: Integer=0;
  FSeriesID: Integer=100;
end;

 Delphi Member Field

Delphi uses the keywords procedure and function. A procedure does not return a value and a function does.

//Interface section:

TCyborg = class(TObject)
public
  procedure IntroduceYourself;
end;

//Implementation section;

procedure TCyborg.IntroduceYourself;
begin
  ShowMessage('Hi, I do not have a name yet.');
end;

//Some event like a button click:

var
  T1: TCyborg;
begin
  T1 := T1.Create;
  T1.IntroduceYourself;
end;

Specify Delphi member modifiers as follows:

reintroduce; overload; [binding modifier]; [calling convention]; abstract; [warning]

The binding modifiers are virtual, dynamic, or override.

The calling conventions are register, pascal, cdecl, stdcall, or safecall.

The warnings are platform, deprecated, or library.

Additional directives include reintroduce, abstract, class, static, overload, and message.

TCyborg = class(TObject)

public

  procedure Speak(pMessage: String); virtual;

end;

 
TSeries888 = class(TCyborg)

public

  procedure Speak(pMessage: String); override;

end;

 Delphi Member Modifiers  

Delphi uses a special property keyword to both get and set the values of properties. The read and write keywords are used to get and set the value of the property directly or through an accessor method. For a read-only property, leave out the write portion of the declaration.

You can give properties any visibility you wish (private, protected, etc). It is common in Delphi to start member fields with "F" ("FName" in our example) and drop the "F" with properties that manage member fields ("Name" in our example).

TCyborg = class(TObject)
private
  FCName: String;
public
  property CyborgName: String read FCName write FCName;
end;

In Delphi, you group member declarations as part of defining the interface for a class in the Interface section of a unit.

Up until D2005, private and protected were not implemented strictly. Starting with D2005, a traditional strict versions of OOP are supported using the strict keyword. OO purist will want you to use strict private over private and strict protected over protected. I suggest you follow that advice until you both fully understand the differences and have a specific need.

Delphi offers a special published specifier which is the same as public members but runtime type information (RTTI) is generated.

TCyborg = class(System.Object)
private
  //Don't use accept when you really want private friendly members.
strict private
  //Use as your default private members.

  FName: String;
protected
  //Don't use accept when you really want protected friendly members.

strict protected
  //Use as your default protected members.

public

  

published

  //RTTI Info

end;

 Delphi Member Visibility  

 Ref: /ASPSuite/KB/Document_View.asp?QID=100889

Delphi for Win32 supports abstract class members using the abstract keyword. You can even instantiate instances of a class that contains abstract members. Then you override each abstract member in a descendant class with Override.

Delphi does not support setting an entire class as abstract. You can create an abstract class (a class with one or more abstract methods), but there is no way to tell the compiler to not allow the instantiation of the abstract class.

Delphi does not support abstract member properties directly. To implement an abstract properity, make use of abstract methods. That is, you can read a GetPropertyX abstract function and write to a SetPropertyX abstract procedure. In effect, creating  an abstract property.

TCyborg = class(TObject)
public
  procedure Speak(pMessage: String); virtual; abstract;
  procedure Walk; virtual; abstract;
end;

TSeries600 = class(TCyborg)
public
  procedure Speak(pMessage: String); override;
  procedure Walk; override;
end;

 Delphi Abstraction (abstract, override)

Delphi allows you to extend an existing class without using inheritance. Buggy in 2005 and not officially supported but stable, usable, and officially supported in 2006 and above.

You declare a class helper similiar to how you declare a class but use the keywords class helper for.

TCyborg = class(TObject)
public
  FCyborgName: String;
end;

TCyborgHelper = class helper for TCyborg
  procedure ShowClassName;
end;

 Delphi Class Helpers (class helper for)  

Delphi does not offer built-in Design by Contract features. It does offer an Assert method which tests if an expression is true. If false, an EAssertionFailed exception is raised. Although you can use Assert in a similar manor as you would use a pre-condition contract, the Delphi help clearly says Assert is a debugging tool only and to not use it in production code.

//Although not intended as a code contract feature,

//Assert is useful for debugging.

method Cyborg.Walk(pPace);

begin
  Assert(pPace > 0);
  Assert(pPace < 100);

  //Overloaded version with message.
  Assert(FEnergyLevel >= 10, 'Energy level too low.');
end;

In Delphi, use the constructor keyword to signify which method or methods are constructors for a class. It is traditional but not required to use a procedure called Create.

In addition to having multiple named constructors, you can overload constructors.

//Interface section.

TCyborg = class(TObject)
public
  constructor Create;
end; 

constructor TCyborg.Create;
begin
  inherited;  //Call the parent Create method

end;

 Delphi Constructors (constructor)  

Object Pascal uses a standard virtual destructor named Destroy which is called by the standard Free method. All objects are dynamic, so you need to call MyObject.Free method or the FreeAndNil(MyObject) routine for each object you create.

Syntax Example:   var MyObject: TObject; begin MyObject := TObject.Create; //Use it... MyObject.Free //Or use...FreeAndNil(MyObject); end;

Delphi does not support multiple implementation inheritance. Each class can have only one parent class (a single inheritance path).

In Delphi, you can use multiple interface usage to design in a multiple class way horizontally in a class hierarchy.

In Delphi, you use interfaces for both com objects and language interfaces and make use of IUnknown, IInterface, and/or TInterfacedObject.

For a pure language interface, add your specified proprieties, procedures, and functions to an interface that descends from IInterface (the base interface) as an interface, no implementation. Then have your implementing class inherit from TInterfacedObject and implement the interface.

For extending the VCL, you descend from the class you wish to extend, then implement an interface from IInterface and add the required functions QueryInterface, _AddRef, and _Release methods (refer to TInterfacedObject for an example).

For a com object, you descend from IUnknown. Descending from IUnknown instead of IInterface informs the Delphi compiler that the interface must be compatible with COM objects -- a Windows feature).

When defining an interface, define it in the type block just like you do for a class but you use the interface keyword instead of the class keyword and in the interfaces section only. Since interfaces, by definition, do not have any implementation details, all you do is specify it in the type block. Then implement in all classes that support the interface.

//Language interface:

//Interface section of unit.

IHuman = Interface(IInterface)
  //Specify interface methods and properties here.

end;

TCyborg = class(TInterfacedObject)

end;

TCyborgHuman = class(TCyborg, IHuman)
  //Specify each here and implement in
  //implementation section.
end;

 Delphi Interfaces (IInterface, TInterfacedObject)

In Delphi, you specify a virtual method with the virtual keyword in a parent class and extend (or replace) it in a descendant class using the override keyword. Call Inherited in the descendant method to execute the code in the parent method.

TRobot = class(TObject)
public
  procedure Speak; virtual;
end;

TCyborg = class(TRobot)
  procedure Speak; Override;
end;

 Delphi Overriding (virtual, override)

As of Delphi 2009, partial classes are not supported. The main reason given in the thread below was that the Delphi compiler is a single pass compiler. Here is a link to a discussion thread on the subject:

• Delphi language (partial classes)

Delphi supports the following types of polymorphism:

• Parametric Polymorphism (Method Overloading)
• Inheritance-Based Polymorphism
• Interface-Based Polymorphism (Interfaces)
• Ad-Hoc Polymorphism (Operator Overloading)

With Delphi, use the sealed keyword to prevent a class from being inherited from and use the final keyword to prevent a method from being overridden.

type

  Robot = class sealed(TObject)
  public
    procedure Speak(pSentence: String); virtual; final;
  end;

 Delphi Sealed class (sealed, final)  

Object Pascal supports static methods, but not static member fields. For static member fields, use traditional Pascal-like global variables.

Since Object Pascal is a hybrid language, you can use global functions and data so the need for class methods is diminished but still useful. For example, since Object Pascal does not have automatic reference counting, you could use a class method to keep track of the number of object instances.

Delphi 1-7: All classes in a unit are friendly (see eachother's private members), some developers like to put each class in it's own unit and reserve putting multiple classes in the same unit until they wish to implement friendly classes.

Delphi 2005+: New strict keyword allows you to indicate friendly.

Delphi Prism: The Strict keyword was introduced from the beginning (Delphi.Net preview that shipped with D7).

type
TMyUtils = class(TObject)
public
  class function MyStaticMethod: Integer;
end;

class function TMyUtils.MyStaticMethod: Integer;

 Delphi Class Members (Class)