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   ► KBProgrammingDelphi PrismLanguage Basics   Print This     
  From the December 2013 Issue of Prestwood eMag
 
Prism Language Basics:
Delphi Prism Parameters (var, const, out)
 
Posted 11 years ago on 12/21/2008 and updated 1/21/2009
Prism Code Snippet:
 A flashcard from our Prism Flashcards Library
 A code snippet from our Prism Code Snippets Page

KB101748

Delphi Prism Parameters

Defining
Prism 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).

By Reference or Value (and by constant and out)
The default for parameters is by value. For by reference, add var in front of the parameter. Prism 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.) Finally, Prism offers an out parameter type which is like a var parameter except it does not have to be initialized prior.

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

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Code Contributed By Mike Prestwood:

Mike Prestwood is a drummer, an author, and creator of the PrestwoodBoards online community. He is the President & CEO of Prestwood IT Solutions. Prestwood IT provides Coding, Website, and Computer Tech services. Mike has authored 6 computer books and over 1,200 articles. As a drummer, he maintains play-drums.com and has authored 3 drum books. If you have a project you wish to discuss with Mike, you can send him a private message through his PrestwoodBoards home page or call him 9AM to 4PM PST at 916-726-5675 x205.

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Linked Certification Question(s)

The following are practice certification questions with answers highlighted. These questions were prepared by Mike Prestwood and are intended to stress an important aspect of this KB post. All our practice questions are intended to prepare you generally for passing any certification test as well as prepare you for professional work.

Beginner

1 Beginner Level Question

Question #1: True or False?

The default for parameters for methods is by reference.

Answer:
  • True
  • False

  •  KB Article #101748 Counter
    11447
    Since 12/21/2008

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