Issue with Code Contract in c#

Question

I am facing a problem that I can not figure out.

Say I have two methods: public void Method1(object obj) in ViewModel class and public void Method2(object obj) in Model class.

Method2 gets called from Method1 using the instance of Model class(say, objM is the object of Model class and a member of ViewModel class).

class ViewModel
{
public void Methods1(object obj)
{
     if (!(
                        (      (false == this.HasSal)
                            && (typeof(Class1) == obj.GetType())
                          )
                    ||
                        (      (true == this.HasSal)
                            && (typeof(Class2) == obj.GetType())
                        )
                   ) 
                )
            {
                throw new ArgumentException("invalid obj");
            }
            Contract.EndContractBlock();
            objM.Method2(obj);
            .....
} 
}

class Model
{
public void Method2(object obj)
{
 Contract.Requires(
                    (      (false == this.HasSal)
                        && (typeof(Class1) == obj.GetType())
                    )
                ||
                    (      (true == this.HasSal)
                        && (typeof(Class2) == obj.GetType())
                    )

            );
    .....
    }
}

Now whenever I try to build the code, Visual studio produces following warning

Code contracts: Requires unproven
(
                    (      (false == this.HasSal)
                        && (typeof(Class1) == obj.GetType())
                    )
                ||
                    (      (true == this.HasSal)
                        && (typeof(Class2) == obj.GetType())
                    )

            )

Please suggest.

try this [link](http://stackoverflow.com/questions/4951813/net-4-code-contracts-requires-unproven-source-null) — RTRokzzz, Jan 23 '13 at 06:56
Please provide details on `HasSal` if possible. Is it a field or property? Is it readonly or [Pure]? — Dandy, Aug 22 '13 at 18:20

score 0 · Answer 1 · edited Jun 20 '20 at 09:12

0

As rtrokzzz have given link to another SO question .NET 4 Code Contracts: “requires unproven: source != null” in comments

Solution for you is to add Contract.Ensures in Method1() and Method2()

Please note: I have not used Code Contracts but I believe from my understanding that code will be as

Contract.Ensures(obj != null);

Update

Contract.Requires(obj != null);

Refer: How to avoid “source !=null” when using Code Contracts and Linq To Sql?

edited Jun 20 '20 at 09:12

Community

1
1

answered Jan 23 '13 at 07:25

Harsh Baid

7,199
5
48
92

Refer the link here for some step-wise information on working with code contracts http://devjourney.com/blog/code-contracts-part-1-introduction/ – Harsh Baid Jan 23 '13 at 07:31
This is another good link: [Better code with C# code contracts](http://www.develop.com/csharpcodecontracts). – Alex Filipovici Jan 23 '13 at 07:35
My point is that I have made sure that if the condition mentioned in Code contract of Method2 is not met, then an exception is thrown from method1 before calling Method2 from Method 1. So Visual studio should not produce an warning for that condition. And Contract.Requires(obj != null) statement is already there in both method 1 and method 2. I did not mentioned about that because I thought that can not be an cause of concern. – Anirban Paul Jan 23 '13 at 08:15

Stephen J. Anderson · Answer 2 · 2013-01-24T09:29:23.687

0

I don't believe that the static checker will ever be able to verify your contract, because the type of obj isn't known until run-time - there is no guarantee that only objects of type Class1 or Class2 will be passed to Method1.

It might be possible to prove this by adding additional contracts to methods that call Method1. If you include that code, I might be able to suggest a way to satisfy the static checker.

EDIT: Actually, there's another problem too. If HasSal is a public-setter property, then I'm not sure your contract can be verified - there's always a possibility that another thread could change the value of HasSal in between Method1 being called and the method body being executed.

edited Jan 24 '13 at 09:29

answered Jan 23 '13 at 13:15

Stephen J. Anderson

436
3
6

My point is that I have made sure that if the condition mentioned in Code contract of Method2 is not met, then an exception is thrown from method1 before calling Method2 from Method 1.So in case the condition is not satisfied, method2 is never going to be called. Is not that enough to satisfy that particular code contract in method2 ?? – Anirban Paul Jan 24 '13 at 04:47
No, because by adding a `Contract.EndContractBlock();` to `Method1`, you're turning that `if` statement into an implicit `Contract.Requires` contract, too. And I think it's *that* one that the static checker is saying it can't prove, not the one in `Method2`. If that's what you want to achieve, then I think (but I haven't tested it myself) that removing the `Contract.EndContractBlock();` will remove the warning. – Stephen J. Anderson Jan 24 '13 at 09:12
Actually, I think there's another problem, so I've edited the answer. – Stephen J. Anderson Jan 24 '13 at 09:18
Commenting out Contract.EndContractBlock() is not helping – Anirban Paul Jan 24 '13 at 12:20
But issue with public setter can be the reason. I shall test it and let u know. – Anirban Paul Jan 24 '13 at 12:22

Issue with Code Contract in c#

2 Answers2

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