This presentation provides an overview of the Code Contracts API for .NET, which allows developers to add design-by-contract features like preconditions, postconditions, and object invariants via static and runtime checking. It demonstrates how to set up code contracts in a project, highlights key features like contract inheritance and API documentation generation, and shows examples of the runtime and static checking capabilities. The presentation concludes with a summary of code contracts benefits, links to additional resources, and time for questions.

1. Melbourne Patterns Group Presentation
By Clarence Bakirtzidis (clarenceb@gmail.com)

2. Agenda
 Overview
 Using Code Contracts
 Main Features
 Runtime Contract Checking
 Static Contract Checking
 Demo(s)
 API Reference
 Summary
 Resources
 Questions
* DbC = Design-by-Contract
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3. Overview
 What is the Code Contracts API?
 Library with Static Methods for DbC
 It is a spin-off from the learnings of the
Spec# project
 Obtaining and Installing
 Academic and Commercial Licenses
 Tools Provided
 Integration with Visual Studio
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4. Overview
 What is Design-by-Contract?
 Originated from Eiffel
 Precondition
○ Condition that is checked on entry to method
 Postcondition
○ Condition that is checked on exit of method
 Invariant (constrain state of objects)
○ Condition checked on exit of constructor and
all public methods and properties
 Static (Compile-time) and Runtime checking
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5. Overview
 Benefits of Code Contracts
 Runtime Checking and Improved Testability
 Static Verification
 API Documentation
○ Examples
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6. Using Code Contracts
 .NET 4.0
 Part of the Base Class Library (BCL)
 No additional references required
 .NET 3.5 or earlier
 Separate assembly Microsoft.Contracts.dll
 Need to add reference to assembly in your
projects
 Contract classes contains in:
 System.Diagnostics.Contracts namespace
 Code Snippets for Visual Studio
 e.g. ci [TAB][TAB] => Contract.Requires(…)
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7. Using Code Contracts
Project Properties
Visual Studio Project Properties
• Runtime Checking
• Static Checking
• Contract Reference Assembly
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8. Main Features
 Design-by-Contract
 Runtime Checking
 Static Checking
 Contract Inheritance
 Supports Abstract Methods and Interfaces
 Generate API documentation
 Hooks into XML documentation and inserts
contract requirements (requires, ensures)
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9. Runtime Contract Checking
 Configuration options
 Level of checking
 Only public surface contracts
 Call-site requires
 Custom rewriter methods
 Assembly rewriting via ccrewrite.exe
 Inserts code in project assemblies to enforce
contracts at runtime
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10. Static Contract Checking
 Configuration options
 Null values
 Array bounds
 Arithmetic (div-by-zero)
 Baseline
 Suppress existing warnings in code base
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11. Demo(s)
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Demo

12. API Reference
 Preconditions
 Contract.Requires(…)
 EndContractBlock (“legacy-
requires”)
 Postconditions
 Contract.Ensures(…)
 Contract.Ensures<E>(…)
 Contract.EnsuresOnThrow<E>(…)
 Prestate Values
 Contract.Result<T>()
 Contract.OldValue<T>(…)
 Out Parameters
 Contract.ValueAtReturn<T>(…)
 Invariants
 Contract.Invariant(…)
 Attributes
 Pure
 ContractInvariantMethod
 ContractVerification
 ContractPublicPropertyName
 Quantifiers
 Contract.ForAll
 Contract.Exists
 Interfaces and Abstract Methods
 ContractClass
 ContractClassFor
 Other
 Contract.Assert(…)
 Contract.Assume(…)
 ContractException
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13. Summary
 Code Contracts bring DbC to the .NET framework
 Provides static and runtime checking of:
 Preconditions
 Postconditions
 Object invariants
 Extends generated XML documentation
 Some known issues (still work in progress)
 Build slowdown - will be addressed in future
 Closures - static checking does not work for closures
 Edit-Continue does not work with code contract rewriting
on
 No contracts allowed on delegates
 No contracts on iterators that use “yield” as IL the code
changed into different form (workaround exists for this)
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14. Code Contracts Summary
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15. Resources
 Code Contracts Project
 http://research.microsoft.com/en-
us/projects/contracts/
 MSDN Forum
 http://social.msdn.microsoft.com/Forums/en-
US/codecontracts/threads
 Spec# Project
 http://research.microsoft.com/en-
us/projects/specsharp
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16. Questions
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