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Code Contract (Delphi and Access VBA Cross Reference Guide)

By Mike Prestwood

Delphi versus Access VBA: A side by side comparison between Delphi and Access VBA.

OOP Details

More object oriented (OO) stuff.

Code Contract

[Other Languages] 

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:  "Code Contracts" Not Supported

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);
Assert(pPace > 0);
Assert(pPace < 100);
  //Overloaded version with message.
Assert(FEnergyLevel >= 10, 'Energy level too low.');
Access VBA:  "Code Contracts" Not Supported

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