CodeContracts Invariant is false

Question

VS2010 keeps telling me that a CodeContract.Invariant is false. I can't see how this can possibly be the case

public class BankAccountIdentifierDefinitionVariation_CreateCommandArgs : ValidatedCommandArgs
{
    public string IdentifierCode {get; private set; }
    public string CountryCode {get; private set; }
    public Ems.Infrastructure.Validation.StringValidator Validator {get; private set; }

    private BankAccountIdentifierDefinitionVariation_CreateCommandArgs()
        : base() { }

    public BankAccountIdentifierDefinitionVariation_CreateCommandArgs(
        string identifierCode,
        string countryCode,
        Ems.Infrastructure.Validation.StringValidator validator)
    {
        Contract.Requires(!string.IsNullOrEmpty(identifierCode));
        Contract.Requires(!string.IsNullOrEmpty(countryCode));
        Contract.Ensures(!string.IsNullOrEmpty(this.IdentifierCode));
        Contract.Ensures(!string.IsNullOrEmpty(this.CountryCode));

        this.IdentifierCode = identifierCode;
        this.CountryCode = countryCode;
    }

    [ContractInvariantMethod]
    void ContractInvariants()
    {
        Contract.Invariant(!string.IsNullOrEmpty(IdentifierCode));
        Contract.Invariant(!string.IsNullOrEmpty(CountryCode));
    }
}

The warning is that both invariants are false, which obviously cannot be the case. I have also tried the two following variations.

Contract.Ensures(!string.IsNullOrEmpty(this.IdentifierCode);
if (string.IsNullOrEmpty(identifierCode)) throw new ArgumentNullException...
this.IdentifierCode = identifierCode;

and also

Contract.Ensures(!string.IsNullOrEmpty(this.IdentifierCode));
this.IdentifierCode = identifierCode;
if (string.IsNullOrEmpty(this.IdentifierCode)) throw new ArgumentNullException...

It looks as if the invariant is false because it is possible for me to change the value of the property via its private setter (even though I do not.) Is there a way to deal with this? The properties must remain properties because I am serializing.

What if the object is constructed through its `private` no-arguments constructor? — Damien_The_Unbeliever, Feb 13 '13 at 11:37
Well, it is not. The static analyzer has the ability to see that no part of the class invokes the parameterless constructor (and it does not have to look in other classes except this one). — Alex Shtoff, Feb 13 '13 at 11:40

score 2 · Accepted Answer · answered Feb 13 '13 at 11:41

2

It seems that the static analyzer fails to see that the parameterless constructor is never invoked. Maybe its existance is enough to question your invariant.

Can you remove it altogether? If you already have a constructor, why do you need a private parameterless one?

answered Feb 13 '13 at 11:41

Alex Shtoff

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I was migrating from structs to classes. That was the problem, so thanks! – Peter Morris Feb 13 '13 at 12:11

score 0 · Answer 2 · answered Feb 13 '13 at 11:47

I would expect the private default constructor to be the source of the warning, since executing that would indeed violate the invariant. However since you have a constructor defined there's nothing stopping you from deleting the default constructor. If you define at least one constructor the compiler will not emit a default contructor on your behalf and since you are never using the default constructor there's no reason to have it in the first place

CodeContracts Invariant is false

2 Answers2