VB Classic OOP Details

Although not currently supported, there are plans for the next version of VS.Net and .Net using Requires and Ensures keywords. Look for code contracts in VS.Net 2010 and .Net 4.

• Read About It: Introduction to Code Contracts

If you code with VS.Net 2008 Pro or above and wish to implement contracts now, checkout the following download:

• Managed Contract Tools

//Future syntax may look something like:

string SetAge(int pAge) { 
  Contract.Requires(pAge>0);
}

string GetAge() { 
  Contract.Ensures(Contract.Result() != null);

}

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;

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.

method Cyborg.Walk(pPace);
require
  pPace > 0;

  pPace < 100;

begin
  ensure
    FEnergyLevel >= 10;
end;

Although not currently supported, there are plans for the next version of VS.Net and .Net using Requires and Ensures keywords. Look for code contracts in VS.Net 2010 and .Net 4.

• Read About It: Introduction to Code Contracts

If you code with VS.Net 2008 Pro or above and wish to implement contracts now, checkout the following download:

• Managed Contract Tools