8.0 Statements
1.0 Introduction1.1 Background1.2 Acknowledgments
The Delphi team also contributed heavily to the generation of this document, and indeed, it would not have been possible to create it without their help.
2.0 Source Files2.1 Source-File Naming
If you are translating a C/C++ header file, then your Pascal header translation will usually have the same name as the file you are translating, except it should have a PAS extension. For instance, Windows.h would become Windows.pas. If the rules of Pascal grammar force you to combine multiple header files into a single unit, then use the name of the base unit into which you are folding the other files. For instance, if you fold WinBase.h into Windows.h, then call the resulting file Windows.pas.
2.2 Source-File OrganizationAll Object Pascal units should contain the following elements in the following order:
- Copyright/ID block comment
- Unit Name
- Interface section
- Implementation
- A closing end and a period.
At least one blank line should separate each of these elements.
Additional elements can be structured in the order you find most appropriate, except that the top of the file should always list the copyright first, the unit name second, then any conditional defines, compiler directives or include statements, then the uses clause:
{*******************************************************}
{ }
{ Borland Delphi Visual Component Library }
{ }
{ Copyright (c) 1995,98 Inprise Corporation }
{ }
{*******************************************************}
unit Buttons;
{$S-,W-,R-}
{$C PRELOAD}
interface
uses
Windows, Messages, Classes,
Controls, Forms, Graphics,
StdCtrls, ExtCtrls, CommCtrl;
It does not matter if you place a type section before a const section, or if you mix type and const sections up in any order you choose.
The implementation should list the word implementation first, then the uses clause, then any include statements or other directives:
implementation
uses
Consts, SysUtils, ActnList,
ImgList;
{$R BUTTONS.RES}
2.2.1 Copyright/ID block comment
Every source file should start with a block comment containing version information and a standard copyright notice. The version information should be in the following format:
{*******************************************************}
{ }
{ Widgets Galore }
{ }
{ Copyright (c) 1995,98 Your Company }
{ }
{*******************************************************}
The copyright notice should contain at least the following line:
-
Copyright (c) yearlist CopyrightHolder.
If you are a third party creating a file for use by Borland, you may add your name at the bottom of the copyright notice:
{*******************************************************}
{ }
{ Borland Delphi Visual Component Library }
{ Copyright (c) 1995,99 Borland International }
{ Created by Project JEDI }
{ }
{*******************************************************}
2.2.2 Unit declaration
Every source file should contain a unit declaration. The word unit is a reserved word, so it should be in lower case. The name of the unit should be in mixed upper and lowercase, and must be the same as the name used by the operating system's file system. Example:
-
unit MyUnit;
This unit would be called MyUnit.pas when an entry is placed in the file system.
2.2.3 uses declarations
Inside units, a uses declaration should begin with the word uses, in lowercase. Add the names of the units, following the capitalization conventions used in the declaration found inside the units:
uses MyUnit;
Each unit must be separated from its neighbor by a comma, and the last unit should have a semicolon after it:
uses
Windows, SysUtils, Classes, Graphics, Controls, Forms,
TypInfo;
It is correct to start the uses clause on the next line, as in the previous example, or you may start the list of units on the same line:
uses Windows, SysUtils, Classes, Graphics, Controls, Forms,
TypInfo;
You may format the list of units in your uses clause so that they wrap just shy of 80 characters, or so that one unit appears on each line.
2.2.4 class/interface declarations
A class declaration begins with two spaces, followed by an identifier prefaced by a capital T. Identifiers should begin with a capital letter, and should have capital letters for each embedded word (InfixCaps). Never use tab characters in your Object Pascal source. Example:
TMyClass
Follow the identifier with a space, then an equals sign, then the word class, all in lower case:
TMyClass = class
If you want to specify the ancestor for a class, add a parenthesis, the name of the ancestor class, and closing parenthesis:
TMyClass = class(TObject)
Scoping directives should be two spaces in from the margin, and declared in the order shown in this example:
TMyClass = class(TObject)
private
protected
public
published
end;
Data should always be declared only in the private section, and its identifier should be prefaced by an F. All type declarations should be four spaces in from the margin:
TMyClass = class(TObject)
private
FMyData: Integer;
function GetData: Integer;
procedure SetData(Value: Integer);
public
published
property MyData: Integer read GetData write SetData;
end;
Interfaces follow the same rules as class declarations, except you should omit any scoping directives or private data, and should use the word interface rather than class.
Naming Conventions
MyIdentifier
MyFTPClass
The major exception to this rule is in the case of header translations, which should always follow the conventions used in the header. For instance, write WM_LBUTTONDOWN, not wm_LButtonDown.
Except in header translations, do not use underscores to separate words. Class names should be nouns or noun phrases. Interface or class names depend on the salient purpose of the interface.
-
GOOD type names:
AddressForm, ArrayIndexOutOfBoundsException
BAD type names:
ManageLayout // verb phrase
delphi_is_new_to_me // underscores
3.1 Unit Naming3.2 Class/Interface Naming
TMyType
See also the section on class/interface declarations.3.3 Field Naming
Do not use all caps for const declarations except where required in header translations.
Delphi is created in California, so we discourage the use of notation, except where required in header translations:
CORRECT
FMyString: string;
INCORRECT
lpstrMyString: string;
The exception to the Hungarian notation rule is in enumerated types.
TBitBtnKind = (bkCustom, bkOK, bkCancel, bkHelp,
bkYes, bkNo, bkClose, bkAbort, bkRetry,
bkIgnore, bkAll);
In this case the letters bk are inserted before each element of this enumeration. bk stands for ButtonKind.
When thinking about naming conventions, consider that one-character field names should be avoided except for temporary and looping variables.
Avoid variable l ("el") because it is hard to distinguish it from 1 ("one") on some printers and displays.
3.4 Method NamingMethod names should use the InfixCaps style. Start with a capital letter, and capitalize the first letter of any subsequent word in the name, as well as any letters that are part of an acronym. All other characters in the name are lower case. Do not use underscores to separate words. Note that this is identical to the naming convention for non-constant fields; however it should always be easy to distinguish the two from context. Method names should be imperative verbs or verb phrases.
Examples:
-
// GOOD method names:
ShowStatus, DrawCircle, AddLayoutComponent
// BAD method names:
MouseButton // noun phrase; doesn't describe function
drawCircle // starts with lower-case letter
add_layout_component // underscores
// The function of this method is unclear. Does
// it start the server running (better: StartServer),
// or test whether or not it is running
// (better: IsServerRunning)?
ServerRunning // verb phrase, but not imperative
A method to get or set some property of the class should be called GetProperty or SetProperty respectively, where Property is the name of the property.
Examples:
-
GetHeight, SetHeight
A method to test some boolean property of the class should be called IsVisible, where Visible is the name of the property.
Examples:
-
IsResizable, IsVisible
3.5 Local Variable NamingLocal variables follow the same naming rules as field names, except you omit the initial F, since this is not a Field of an object. (see section 3.3).
3.6 Reserved Words3.7 Type Declarations4.0 White Space Usage
Blank lines can improve readability by grouping sections of the code that are logically related. A blank line should also be used in the following places:
- After the copyright block comment, package declaration, and import section.
- Between class declarations.
- Between method declarations.
4.2 Blank Spaces
4.2.2 Blanks should not be used:
- Between a method name and its opening parenthesis.
- Before or after a .(dot) operator.
- Between a unary operator and its operand.
- Between a cast and the expression being cast.
- After an opening parenthesis or before a closing parenthesis.
- After an opening square bracket [ or before a closing square bracket ].
- Before a semicolon.
Examples of correct usage:
function TMyClass.MyFunc(var Value: Integer);
MyPointer := @MyRecord;
MyClass := TMyClass(MyPointer);
MyInteger := MyIntegerArray[5];
Examples of incorrect usage:
function TMyClass.MyFunc( var Value: Integer ) ;
MyPointer := @ MyRecord;
MyClass := TMyClass ( MyPointer ) ;
MyInteger := MyIntegerArray [ 5 ] ;
4.3 Indentation
There are few exceptions. The reserved words unit, users, type, interface, implementation, initialization and finalization should always be flush with the margin. The final end statement at the end of a unit should be flush with the margin. In the project file, the word program, and the main begin and end block should all be flush with the margin. The code inside the begin..end block, should be indented at least two spaces.
4.4 Continuation Lines
Examples:
-
// CORRECT
function CreateWindowEx(dwExStyle: DWORD;
lpClassName: PChar; lpWindowName: PChar;
dwStyle: DWORD; X, Y, nWidth, nHeight: Integer;
hWndParent: HWND; hMenu: HMENU; hInstance: HINST;
lpParam: Pointer): HWND; stdcall;
// CORRECT
if ((X = Y) or (Y = X) or
(Z = P) or (F = J) then
begin
S := J;
end;
Never wrap a line between a parameter and its type, unless it is a comma separated list, then wrap at least before the last parameter so the type name follows to the next line. The colon for all variable declarations contains no whitespace between it and the variable. There should be a single space following the colon before the type name;
-
// CORRECT
procedure Foo(Param1: Integer; Param2: Integer);
// INCORRECT
procedure Foo( Param :Integer; Param2:Integer );
A continuation line should never start with a binary operator.[???] Avoid breaking a line where normally no white space appears, such as between a method name and its opening parenthesis, or between an array name and its opening square bracket. If you must break under these circumstances, then one viable place to begin is after the opening parenthesis that follows a method name. Never place a begin statement on the same line with any other code.
Examples:
-
// INCORRECT
while (LongExpression1 or LongExpression2) do begin
// DoSomething
// DoSomethingElse;
end;
// CORRECT
while (LongExpression1 or LongExpression2) do
begin
// DoSomething
// DoSomethingElse;
end;
// CORRECT
if (LongExpression1) or
(LongExpression2) or
(LongExpression3) then
5.0 Comments
- It is helpful to place comments near the top of unit to explain its purpose.
- It is helpful to place comments before a class declaration.
- It is helpful to place comments before some method declarations.
- Avoid making obvious comments:
-
i := i + 1; // Add one to i
- Remember that misleading comments are worse than no comments at all.
- Avoid putting any information into comments that is likely to become out of date.
- Avoid enclosing comments in boxes drawn with asterisks or other special typography.
- Temporary comments that are expected to be changed or removed later should be marked with the special tag "???:" so that they can easily be found afterwards. Ideally, all temporary comments should have been removed by the time a program is ready to be shipped.
Example:
// ???: Change this to call Sort when it is fixed
List.MySort;
5.1 Block Comments
{ TPropertyEditor
Edits a property of a component, or list of components,
selected into the Object Inspector. The property
editor is created based on the type of the
property being edited as determined by the types
registered by...
etc...
GetXxxValue
Gets the value of the first property in the
Properties property. Calls the appropriate
TProperty GetXxxValue method to retrieve the
value.
SetXxxValue Sets the value of all the properties
in the Properties property. Calls the appropriate
TProperty SetXxxxValue methods to set the value. }
A block comment is always used for the copyright/ID comment at the beginning of each source file. It is also used to "comment out" several lines of code.
Block comments used to describe a method should appear before the method declaration.
Example:
-
// CORRECT
{ TMyObject.MyMethod
This routine allows you to execute code. }
procedure TMyObject.MyMethod;
begin
end;
// INCORRECT
procedure TMyObject.MyMethod;
{******************************************************
TMyObject.MyMethod
This routine allows you to execute code.
*******************************************************}
begin
end;
A second kind of block comment contains two characters, a parenthesis and an asterisk: (* *). This is sometimes called starparen comments. These comments are generally useful only during code development, as their primary benefit is that they allow nesting of comments, as long as the nest level is less than 2. Object Pascal doesn't support nesting comments of the same type within each other, so really there is only one level of comment nesting: curly inside of starparen, and starparen inside of curly. As long as you don't nest them, any other standard Pascal comments between comments of this type will be ignored. As a result, you can use this syntax to comment out a large chunk of code that is full of mixed code and comments:
(* procedure TForm1.Button1Click(Sender: TObject);
begin
DoThis; // Start the process
DoThat; // Continue iteration
{ We need a way to report errors here, perhaps using
a try finally block ??? }
CallMoreCode; // Finalize the process
end; *)
In this example, the entire Button1Click method is commented out, including any of the subcomments found between the procedure's begin..end pair.
5.2 Single-Line Comments
A single-line comment or comment group should always be preceded by a blank line, unless it is the first line in a block. If the comment applies to a group of several statements, then the comment or comment group should also be followed by a blank line. If it applies only to the next statement (which may be a compound statement), then do not follow it with a blank line.
Example:
-
// Open the database
Table1.Open;
Single-line comments can also follow the code they reference. These comments, sometimes referred to as trailing comments, appear on the same line as the code they describe. They should have at least one space-character separating them from the code they reference. If more than one trailing comment appears in a block of code, they should all be aligned to the same column.
Example:
-
if (not IsVisible) then
Exit; // nothing to do
Inc(StrLength); // reserve space for null terminator
Avoid commenting every line of executable code with a trailing comment. It is usually best to limit the comments inside the begin..end pair of a method or function to a bare minimum. Longer comments can appear in a block comment before the method or function declaration.
Classes
The body of a class declaration should be organized in the following order:
- Field declarations
- Method declarations
- Property declarations
The fields, properties and methods in your class should be arranged alphabetically by name.
6.1.1 Access levels
Except for code inserted by the IDE, the scoping directives for a class should be declared in the following order:
- Private declarations
- Protected declarations
- Public declarations
- Published declarations
There are four access levels for class members in Object Pascal: published, public, protected, and private -- in order of decreasing accessibility. By default, the access level is published. In general, a member should be given the lowest access level which is appropriate for the member. For example, a member which is only accessed by classes in the same unit should be set to private access. Also, declaring a lower access level will often give the compiler increased opportunities for optimization. On the other hand, use of private makes it difficult to extend the class by sub-classing. If there is reason to believe the class might be sub-classed in the future, then members that might be needed by sub-classes should be declared protected instead of private, and the properties used to access private data should be given protected status.
You should never allow public access to data. Data should always be declared in the private section, and any public access should be via getter and setter methods, or properties.
6.1.8 Constructor declarations
Methods should be arranged alphabetically. It is correct either to place your constructors and destructors at the head of this list in the public section, or to arrange them in alphabetical order within the public section.
If there is more than one constructor, and if you choose to give them all the same name, then sort them lexically by formal parameter list, with constructors having more parameters always coming after those with fewer parameters. This implies that a constructor with no arguments (if it exists) is always the first one. For greatest compatibility with C++Builder, try to make the parameter lists of your constructors unique. C++ cannot call constructors by name, so the only way to distinguish between multiple constructors is by parameter list.
6.2 Method DeclarationsExamples:
-
// Broken line is aligned two spaces in from left.
procedure ImageUpdate(Image img, infoflags: Integer,
x: Integer, y: Integer, w: Integer, h: Integer)
InterfacesInterfaces are declared in a manner that runs parallel to the declaration for classes:
-
InterfaceName = interface([Inherited Interface])
InterfaceBody
end;
An interface declaration should be indented two spaces. The body of the interface is indented by the standard indentation of four spaces. The closing end statement should also be indented two characters. There should be a semi-colon following the closing end statement.
There are no fields in an interface declaration. Properties, however, are allowed.
All interface methods are inherently public and abstract; do not explicitly include these keywords in the declaration of an interface method.
Except as otherwise noted, interface declarations follow the same style guidelines as classes.
7.1 Interface Body Organization
- Interface method declarations
- Interface property declarations
The declaration styles of interface properties and methods are identical to the styles for class properties and methods.
8.0 Statements
Here is a simple statement:
A := B;
Here is a compound, or structured, statement:
begin
B := C;
A := B;
end;
8.0.1 Simple Statements
MyValue :=
MyValue + (SomeVeryLongStatement / OtherLongStatement);
8.0.1 Compound Statements
begin
MyStatement;
MyNextStatement;
MyLastStatement // semicolon optional
end;
8.1.1 Assignment and expression statements
Each line should contain at most one statement. For example:
-
a := b + c; Inc(Count); // INCORRECT
a := b + c; // CORRECT
Inc(Count); // CORRECT
8.1.2 Local variable declarations
Local variables should have Camel Caps, that is, they should start with a capital letter, and have capital letters for the beginning of each embedded word. Do not preface variable names with an F, as that convention is reserved for Fields in a class declaration:
var
MyData: Integer;
MyString: string;
You may declare multiple identifiers of the same type on a single line:
var
ArraySize, ArrayCount: Integer;
This practice is discouraged in class declarations. There you should place each field on a separate line, along with its type.
8.1.3 Array declarations
There should always be a space before the opening bracket "[" and after the closing bracket.
type
TMyArray = array [0..100] of Char;
8.2.3 if statement
If statements should always appear on at least two lines.
Example:
-
// INCORRECT
if A < B then DoSomething;
// CORRECT
if A < B then
DoSomething;
In compound if statements, put each element separating statements on a new line:
Example:
-
// INCORRECT
if A < B then begin
DoSomething;
DoSomethingElse;
end else begin
DoThis;
DoThat;
end;
// CORRECT
if A < B then
begin
DoSomething;
DoSomethingElse;
end
else
begin
DoThis;
DoThat;
end;
Here are a few more variations that are considered valid:
-
// CORRECT
if Condition then
begin
DoThis;
end else
begin
DoThat;
end;
// CORRECT
if Condition then
begin
DoThis;
end
else
DoSomething;
// CORRECT
if Condition then
begin
DoThis;
end else
DoSomething;
One that has fallen out of favor but deserves honorable mention:
-
if Condition then
DoThis
else DoThat;
8.2.4 for statement
Example:
-
// INCORRECT
for i := 0 to 10 do begin
DoSomething;
DoSomethingElse;
end;
// CORRECT
for i := 0 to 10 do
begin
DoSomething;
DoSomethingElse;
end;
8.2.5 while statement
Example:
-
// INCORRECT
while x < j do begin
DoSomething;
DoSomethingElse;
end;
// CORRECT
while x < j do
begin
DoSomething;
DoSomethingElse;
end;
8.2.6 repeat until statement
Example:
-
// CORRECT
repeat
x := j;
j := UpdateValue;
until j > 25;
8.2.7 case statement
Example:
-
// CORRECT
case Control.Align of
alLeft, alNone: NewRange := Max(NewRange, Position);
alRight: Inc(AlignMargin, Control.Width);
end;
// CORRECT
case x of
csStart:
begin
j := UpdateValue;
end;
csBegin: x := j;
csTimeOut:
begin
j := x;
x := UpdateValue;
end;
end;
// CORRECT
case ScrollCode of
SB_LINEUP, SB_LINEDOWN:
begin
Incr := FIncrement div FLineDiv;
FinalIncr := FIncrement mod FLineDiv;
Count := FLineDiv;
end;
SB_PAGEUP, SB_PAGEDOWN:
begin
Incr := FPageIncrement;
FinalIncr := Incr mod FPageDiv;
Incr := Incr div FPageDiv;
Count := FPageDiv;
end;
else
Count := 0;
Incr := 0;
FinalIncr := 0;
end;
8.2.8 try statement
Example:
-
// Correct
try
try
EnumThreadWindows(CurrentThreadID, @Disable, 0);
Result := TaskWindowList;
except
EnableTaskWindows(TaskWindowList);
raise;
end;
finally
TaskWindowList := SaveWindowList;
TaskActiveWindow := SaveActiveWindow;
end;
-