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![Justification :)
WATCH OUT
CODE SNIPPET
Unit tests
Are limited and time
consuming to
support
[Test]
public void PressEquals_AddingTwoPlusTwo_ReturnsFour()
{
// Arrange
decimal value1 = 2m;
decimal value2 = 2m;
decimal expected = 4m;
var calculator = new Calculator();
// Act
calculator.Enter(value1);
calculator.PressPlus();
calculator.Enter(value2);
calculator.PressEquals();
decimal actual = calculator.Display;
// Assert
Assert.AreEqual(expected, actual,
"When adding {0} + {1}, expected {2} but found
{3}.", value1, value2, expected, actual);
}](https://image.slidesharecdn.com/designbycontract-140114170802-phpapp01/85/Code-Contracts-9-320.jpg)
![Code Contracts
WHAT IS IT?
CODE SNIPPET
Pre-conditions
class WebService
{
private IWarehouse store;
public WebService(IWarehouse store)
{
Contract.Requires(store != null);
Contract.Ensures(this.store != null);
Post-conditions
this.store = store;
}
[ContractInvariantMethod]
private void ObjectInvariant()
{
Contract.Invariant(this.store != null);
}
Invariants
}](https://image.slidesharecdn.com/designbycontract-140114170802-phpapp01/85/Code-Contracts-21-320.jpg)
Uploaded byAlexei Skachykhin
Code Contracts
The document discusses the concept of 'Design by Contract' (DbC) and its implementation in software development, highlighting the challenges of unit testing, documentation, and assertions. It introduces Microsoft's Code Contracts as a .NET implementation of DbC, detailing its features such as pre-conditions, post-conditions, invariants, and automatic documentation generation. The document also outlines the benefits of using DbC, including improved testability and runtime checking, while acknowledging potential challenges in static analysis and tool reliability.
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Code Contracts
- 1. DESIGN BY CONTRACT WITH CODECONTRACTS
- 2.
- 3. Confession :( “How manyof you do write unit tests?”
- 4. Confession :( “How manyof you do write documentation?”
- 5. Confession :( “How manyof you do write asserts?”
- 6.
- 7. Justification :) THE GOODPART “At some extent all of these tools don`t work in a real life.” - me
- 8. Justification :) WATCH OUT Documentation Nodocumentation is better than bad documentation CODE SNIPPET //declare variable foo as an integer and //set it to three. private int foo = 3;
- 9. Justification :) WATCH OUT CODESNIPPET Unit tests Are limited and time consuming to support [Test] public void PressEquals_AddingTwoPlusTwo_ReturnsFour() { // Arrange decimal value1 = 2m; decimal value2 = 2m; decimal expected = 4m; var calculator = new Calculator(); // Act calculator.Enter(value1); calculator.PressPlus(); calculator.Enter(value2); calculator.PressEquals(); decimal actual = calculator.Display; // Assert Assert.AreEqual(expected, actual, "When adding {0} + {1}, expected {2} but found {3}.", value1, value2, expected, actual); }
- 10. Justification :) WATCH OUT CODESNIPPET public string Substring(int startIndex, int length) Asserts Make little use for calling code CODE SNIPPET public string Substring(int startIndex, int length) { if (startIndex < 0) throw new ArgumentOutOfRangeException("startIndex"); if (startIndex > this.Length) throw new ArgumentOutOfRangeException("startIndex"); if (length < 0) throw new ArgumentOutOfRangeException("length"); if (startIndex > this.Length - length) throw new ArgumentOutOfRangeException("length"); if (length == 0) return string.Empty; else return this.InternalSubStringWithChecks(startIndex, length, false); }
- 11. Consequences ABANDONING “If so, whywouldn`t I abandon all this crap?”
- 12. Consequences PROGRAMMING BY COINCIDENCE “Weshould avoid programming by coincidence - relying on luck and accidental successes - in favor of programming deliberately.” - Dave Thomas
- 13. Design by Contract WHATIS IT? “A way of designing software, which implies formal and precise specifications for software components with pre-conditions, post-conditions and invariants in source code itself.” Bertrand Meyer EIFFEL PL, 1986
- 14. Design by Contract EIFFEL CODESNIPPET Pre-conditions Post-conditions connect_to_server (server: SOCKET) -- Connect to a server. require server /= Void and then server.address /= Void do server.connect ensure connected: server.is_connected end CODE SNIPPET class Invariants DATE invariant valid_day: 1 <= day and day <= 31 valid_hour: 0 <= hour and hour <= 23 end
- 15. Design by Contract RULES Metaphor: Client, Supplier agree on a Contract 1 2 3 The supplier must provide a certain product (obligation) and is entitled to expect that the client has paid its fee (benefit). The client must pay the fee (obligation) and is entitled to get the product (benefit). Both parties must satisfy certain obligations, such as laws and regulations, applying to all contracts.
- 16. Design by Contract WHY? “Whatare the benefits?” Discoverability of your API Improved testability Runtime & Static Checking Automatic generation of documentation
- 17. Design by Contract IMPLEMENTATIONSFOR .NET “Do we have similar concept in modern programming languages? Lets ask Microsoft.”
- 19.
- 20. Code Contracts WHAT ISIT? “Microsoft`s implementation of Design by Contract for .NET. Proposed back in 2008.”
- 21. Code Contracts WHAT ISIT? CODE SNIPPET Pre-conditions class WebService { private IWarehouse store; public WebService(IWarehouse store) { Contract.Requires(store != null); Contract.Ensures(this.store != null); Post-conditions this.store = store; } [ContractInvariantMethod] private void ObjectInvariant() { Contract.Invariant(this.store != null); } Invariants }
- 22. Code Contracts COMPLETE API “Mostlyit is nice and easy, but occasionally it can be mind blowing.”
- 23. Code Contracts COMPONENTS CCRewrite CCCheck CCDocGen Binary Rewriter StaticChecker XML Doc Extender
- 24. Code Contracts RUNTIME CHECKING WebService.cs publicWebService(IWarehouse store) { Contract.Requires(store != null); Contract.Ensures(this.store != null); this.store = store; WebService.dll IL from requires } csc/vbc/… + ccrewrite IL from body IL from ensures
- 25. Code Contracts RUNTIME CHECKING(GENERAL CLIENTS) WebService.cs public WebService(IWarehouse store) { Contract.Requires(store != null); Contract.Ensures(this.store != null); this.store = store; } WebService.dll IL from requires csc/vbc/… + ccrewrite IL from body
- 26. Code Contracts RUNTIME CHECKING(TRUSTED CLIENTS) WebService.cs public WebService(IWarehouse store) { Contract.Requires(store != null); Contract.Ensures(this.store != null); this.store = store; } WebService.dll csc/vbc/… IL from body
- 27. Code Contracts DOCUMENTATION GENERATION WebService.xml <member name="M:PDC.WebService.#ctor(PDC. IWarehouse)"> <summary>Constructsa new instance for processing orders against the specified warehouse.</summary> <param name="store">The warehouse this instance is to use. </param> </member> WebService.xml ccdocgen WebService.Contracts.dll IL from requires IL from ensures <member name="M:PDC.WebService.#ctor(PDC.IWarehouse)"> <summary>Constructs a new instance for processing orders against the specified warehouse.</summary> <param name="store">The warehouse this instance is to use. </param> <requires> store != null </requires> <ensures> this.store != null </ensures> </member>
- 28. Code Contracts CONTRACT REFERENCEASSEMBLIES “Companion assemblies generated at compile time and contain only contract portion of types.”
- 29. Code Contracts ANNOYANCES 1 2 3 Static analysisis usually slow Tools are failing from time to time No way to execute post-conditions under lock statement
- 30. References Code Contracts http://msdn.microsoft.com/en-us/magazine/ee236408.aspx Code Contractson Microsoft Research http://research.microsoft.com/en-us/projects/contracts/ Code Contracts on MSDN http://msdn.microsoft.com/en-us/library/dd264808.aspx Code Contracts in C# http://www.infoq.com/articles/code-contracts-csharp
- 31.