CodeContracts – Amazing… simply amazing

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Look at this code… looks perfectly normal right?  In a code review, you wouldn’t notice anything amiss.

 var tags = new List<DataCacheTagContract>();
tags.Add(new DataCacheTagContract() { Tag = "tag" });
tags.Add(new DataCacheTagContract()); 

Add("key", "value", TimeSpan.FromSeconds(1), tags);

But there is a bug present and it isn’t obvious…  How would you know?  Code Contracts saved the day.  When I ran the unit test that this code comes from I got a test failure.

 
Exception message: System.Diagnostics.Contracts.__ContractsRuntime+ContractException: Postcondition failed: Contract.Result<string>() != null

Strange I thought… I didn’t realize I had a contract on the DataCacheTagContract class but I do – it is an inherited contract and because I’ve installed a  VS2010 extension that the team is developing that shows me inherited contracts I can see what is going on.

DataCacheTagContract overrides ToString()

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The CodeContracts extension shows me that I’ve inherited contracts because I’m overriding this method.  Do you realize how amazing this is?  I’m overriding a method and even though I don’t know the semantics of the method I’m overriding as well as I should, CodeContracts knows and applies them. 

I click on the Contracts inherited from Object text and it shows me that ToString() should never return null.

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How many bugs exist in code because somebody overrides a method and silently breaks the semantic of the method by the way it was implemented.  With CodeContracts I can supply tools that will help them to know when they are doing this.  Wow – I never want to write code without CodeContracts ever again.