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Rock Your Code With Code Contracts -2013
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Rock Your Code With Code Contracts -2013

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This session will introduce developers to the new powerful new feature that is part of the .NET 4.5 framework called Code Contracts. Code Contracts brings the advantages of design-by-contract......

This session will introduce developers to the new powerful new feature that is part of the .NET 4.5 framework called Code Contracts. Code Contracts brings the advantages of design-by-contract programming to .NET programming. Contracts are used to improve testing via run-time checking, enable static contract verification, and documentation generation.

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  • 1. David McCarter dotnetdave@live.com
  • 2. About David McCarter •Microsoft MVP •David McCarter’s .NET Coding Standards •http://codingstandards.notlong.com/ •dotNetTips.com •700+ Tips, Tricks, Articles, Links! •Open Source Projects: •http://codeplex.com/dotNetTips •San Diego .NET Developers Group •www.sddotnetdg.org •UCSD Classes •http://dotnetdaveclasses.notlong.com @realdotnetdave davidmccarter dotnetdave@live.com
  • 3. Conference DVD’s • Rock Your Technical Interview DVD • Full length video of session • Expert Videos • Engineer Videos • Interview Questions • Slide deck • More! • Rock Your Code DVD • Videos of sessions • Sides, sample code • More!
  • 4. Overview Introducing Code Contracts Pre-conditions & Post-conditions Contract Your Types With Contracts Summary
  • 5. Overview
  • 6.    Always check for valid parameter arguments! Perform argument validation for every public or protected method Throw meaningful exceptions to the developer for invalid parameter arguments   Use the System.ArgumentException class Or your own class derived from System.ArgumentException
  • 7. public string FormatPhoneNumber(string str, bool bTakeOutDash) { string str1 = str.Trim(); if (bTakeOutDash) { if (11 == str.Length && -1 != str.IndexOf('-')) { str1 = ""; for (int i = 0; i < str.Length; i++) { if ("-" != str.Substring(i, 1)) { str1 = string.Concat(str1, str.Substring(i, 1)); } } } } return str1; }
  • 8. public string FormatPhoneNumber(string str, bool bTakeOutDash) { if (string.IsNullOrWhiteSpace(str)) { throw new ArgumentNullException("str", "Phone number must be supplied."); } string str1 = str.Trim(); if (bTakeOutDash) { // Code Removed for brevity } return str1; }
  • 9. Introducing Code Contracts Build Better Types
  • 10.    Is an approach for designing software. It prescribes that software designers should define formal, precise and verifiable interface specifications for software components, which extend the ordinary definition of abstract data types with preconditions, post-conditions and invariants. These specifications are referred to as "contracts", in accordance with a conceptual metaphor with the conditions and obligations of business contracts.
  • 11.  A discipline of analysis, design, implementation, management  Applications throughout the software lifecycle:  Getting the software right:        analysis, design , implementation Debugging & testing Automatic documentation Getting inheritance right Getting exception handling right! Maintenance Management
  • 12.  Every software element is intended to satisfy a certain goal, or contract   For the benefit of other software elements (and ultimately of human users) The contract of any software element should be   Explicit Part of the software element itself
  • 13. Precondition  What does it expect? Postcondition  What does it promise?  What does it maintain? Class invariant
  • 14.      New API + tools from Microsoft for Designby-Contract System.Diagnostics.Contracts MSIL rewriting Inspired by Spec# Included in .NET 4.0/ 4.5  Latest version released 9/13  http://research.microsoft.com/en-us/projects/contracts/
  • 15. Pre-conditions Post-conditions Oh My!
  • 16.     Usually for method parameter checking Caller’s responsibility to make sure the precondition is true on entry into method Does not need to be compiled in production code Can also include throwing of Exceptions  These must be compiled into assembly
  • 17. public static string FormatPhoneNumber(string str, bool bTakeOutDash) { Contract.Requires(string.IsNullOrWhiteSpace(str) == false); string str1 = str.Trim(); // code removed for brevity return str1; }
  • 18. public static string FormatPhoneNumber(string str, bool bTakeOutDash) { Contract.Requires<ArgumentNullException> (string.IsNullOrWhiteSpace(str) == false); string str1 = str.Trim(); // code removed for brevity return str1; }
  • 19.    Postconditions are contracts for the state of a method when it terminates The postcondition is checked just before exiting a method The run-time behavior of failed postconditions is determined by the runtime analyzer.
  • 20. public static string FormatPhoneNumber(string str, bool bTakeOutDash) { Contract.Requires(string.IsNullOrWhiteSpace(str) == false); Contract.Ensures(string.IsNullOrEmpty(Contract.Result<string>()) ==false); string str1 = str.Trim(); // code removed for brevity return str1; }
  • 21.    Contract.EnsuresOnThrow<T> Contract.OldValue Contract.ForAll   Collections Contract.Ensures  Out parameters
  • 22. Contract Your Types With Contracts Creates MUCH Better Types!
  • 23.  ContractInvariantMethod     Mark methods that contain object invariant specifications The methods marked with this attribute must be nullary methods with void return types and contain nothing other than calls to Contract You may not call these methods from within your code. Force coders to do proper value checking!
  • 24. public Int32 Value { get { return _value; } private set { if (this.Value != value) { if ((value <= this.Maximum) && (value >= this.Minimum)) { this._value = value; this.OnValueChanged(); } } } }
  • 25. public Int32 Value { get { return _value; } private set { if (this.Value != value) { Contract.Requires<ArgumentOutOfRangeException>(value >= 0); if ((value <= this.Maximum) && (value >= this.Minimum)) { this._value = value; this.OnValueChanged(); } } } }
  • 26. private Int32 _value; [ContractInvariantMethod] private void Invariants() { Contract.Invariant(_value >= 0, "Value cannot be less than zero."); } -------------------------------------set { // Contract.Requires<ArgumentOutOfRangeException>(value >= 0); if (this.Value != value) { // Code Removed for Brevity } }
  • 27. Summary
  • 28.  Pex and Moles     Isolation and White box Unit Testing for .NET Pex auto generates test suites with high code coverage Moles supports unit testing by way of detours and stubs (delegates) http://research.microsoft.com/en-us/projects/pex/
  • 29.  Microsoft Research   http://research.microsoft.com/enus/projects/contracts/ Channel 9  http://channel9.msdn.com/Search/?Term=code %20contracts
  • 30. Questions? All Pictures & Videos © David McCarter •Presentation Downloads •slideshare.com/dotnetdave •Please Rate My Session: •speakerrate.com/dotnetdave •David McCarter’s •.NET Coding Standards •dotnettips.com •Geek Swag •geekstuff.notlong.com @realdotnetdave davidmccarter dotnetdave@live.com