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   ► KBTo/From GuidesDelphi Prism  Print This     

Code Contract (Delphi Prism and C++ Cross Reference Guide)

By Mike Prestwood

Delphi Prism versus C++: A side by side comparison between Delphi Prism and C++.

 
OOP Details
 

More object oriented (OO) stuff.

Code Contract

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A.k.a. Class Contract and Design by Contracts.

A contract with a method that must be true upon calling (pre) or exiting (post). A pre-condition contract must be true when the method is called. A post-condition contract must be true when exiting. If either are not true, an error is raised. For example, you can use code contracts to check for the validity of input parameters, and results

An invariant is also a code contract which validates the state of the object required by the method.

Delphi Prism:  "Class Contracts" require, ensure

Prism supports class contracts with its require and ensure keywords. The require keyword is a pre condition that must be true when the method is called. The ensure keyword is a post condition that must be true when a method exits. With either, if the condition evaluates to false, then an assertion is generated.

The require and ensure keywords will expand the method body to list the preconditions; both sections can contain a list of Boolean statements, separated by semicolons.

Syntax Example:
method Cyborg.Walk(pPace);
require
pPace > 0;
  pPace < 100;
begin
ensure
FEnergyLevel >= 10;
end;
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