So do C#4.0 Code Contracts Actually Do Anything?

Question

After reading about the System.Diagnostics.Contracts.Contract static class that has been influenced by the awesomeness of Spec# I was thrilled and immediately started peppering my code with calls to Contract.Requires() and Contract.Ensures().

I guess it's just because my code is so super-awesome and bug-free that checking that those calls actually did something just didn't come up until recently. A bug slipped through and I came to the realization that these calls do not do anything! I would have thought that they at least throw an exception when the condition is violated but no such luck.

Am I missing something? Does anyone know what the heck is the point?

score 17 · Accepted Answer · answered May 21 '10 at 16:22

From the Contract Class page at MSDN:

You must use a binary rewriter to insert run-time enforcement of contracts. Otherwise, contracts such as the Contract.Ensures method can only be tested statically and will not throw exceptions during run time if a contract is violated. You can download the binary rewriter CCRewrite from Code Contracts on the MSDN DevLabs Web site. CCRewrite comes with a Visual Studio add-in that enables you to activate run-time contract enforcement from the project Properties page. The binary rewriter and the Visual Studio add-in do not ship with Visual Studio 2010 or the Windows SDK.

score 2 · Answer 2 · answered Sep 24 '13 at 21:13

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Expanding on JSBangs' answer:

You must check the "Perform Runtime Contract Checking" box here:

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(I also checked the "Static Checking > Peform Static Contract Checking" box)

answered Sep 24 '13 at 21:13

B. Clay Shannon-B. Crow Raven

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Also of note, the [code contracts visual studio extensions](http://visualstudiogallery.msdn.microsoft.com/02de7066-b6ca-42b3-8b3c-2562c7fa024f) which will attempt to parse your contracts and inform you of issues before you even build. – George Mauer Sep 24 '13 at 22:42

score 0 · Answer 3 · answered May 21 '10 at 16:23

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If you want the .Requires call to throw an error you need to set an option in project settings or use .Requires<T> call

answered May 21 '10 at 16:23

unclepaul84

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What do you mean? What option? I am using .Requrires() – George Mauer May 21 '10 at 16:23
Under project properties, head to the "Code Contracts" tab. – porges May 26 '10 at 01:25

So do C#4.0 Code Contracts Actually Do Anything?

3 Answers3