Code Contracts: IEnumerator <T> .GetEnumerator () weird inherited contract?

Question

I use Code Contracts with the VS2010 Extension Code Contract Editor. I have a class that implements an interface IEnumerable<T>, and I realized the iterator block for the method GetEnumerator(). Above it, I see the following inherited contract:

I understand the first and third requirement of the contract - GetEnumerator()it should never return null, and it should never cause a side effect. But what does the second requirement of the contract mean? What is this Modelproperty IEnumerator<T>and IEnumerable?

EDIT: As Damien_The_Unbeliever noted in his comment, the contract for IEnumerable<T>and IEnumerator<T>is in a separate file - the assembly of contracts. Using Reflector , when disassembling the contract of these two interfaces (full code here ), you can see the following:

[return: Fresh]
[Escapes(true, false), Pure, GlobalAccess(false)]
public IEnumerator GetEnumerator()
{
    IEnumerator enumerator;
    Contract.Ensures((bool) (Contract.Result<IEnumerator>() != null), null, "Contract.Result<IEnumerator>() != null");
    Contract.Ensures((bool) (Contract.Result<IEnumerator>().Model == this.Model), null, "Contract.Result<IEnumerator>().Model == this.Model");
    Contract.Ensures((bool) (Contract.Result<IEnumerator>().CurrentIndex == -1), null, "Contract.Result<IEnumerator>().CurrentIndex == -1");
    return enumerator;
}

Interestingly, there GetEnumerator()is an additional contract that is not displayed by the editor extension:

Contract.Result<IEnumerator>().CurrentIndex == -1

And some additional secrets (such as attributes Fresh, Escapesand GlobalAccess).

Answer 1

/​​, C:\Program Files\Microsoft\Contracts\Contracts.NETFramework\v4.0\mscorlib.Contracts.dll( ).

, . , , -, , , (), IEnumerator, . "" GetEnumerator Reset, MoveNext .

, . , - ContractModel, , , , .

---

..:

MoveNext IEnumerator - , , MoveNext Model (, , , GetEnumerator), CurrentIndex 0 Model.Length. /. , .