c# - 代码契约(Contract) : Ensures Unproven & Requires Unproven

Question

我不确定我是否在这里做错了什么或者是否需要修复...

我有一个自定义的 Dictionary 包装器类，这里是一段必要的代码。

public int Count
{
    get
    {
        Contract.Ensures(Contract.Result<int>() >= 0);

        return InternalDictionary.Count;
    }
}

public bool ContainsKey(TKey key)
{
    //This contract was suggested by the warning message, if I remove it
    //I still get the same warning...
    Contract.Ensures(!Contract.Result<bool>() || Count > 0);

    return InternalDictionary.ContainsKey(key);
}

我为 ContainsKey 添加行的唯一原因是因为我收到以下警告消息(现在仍然如此):Codecontracts: ensures unproven: !Contract.Result<bool>() || @this.Count > 0 .我可以删除此行并仍然得到 SAME ISSUE!

我该怎么做才能摆脱这些问题？

---

更新:

我也试过(按照建议)...

public Boolean ContainsKey(TKey key)
{
    Contract.Requires(Count == 0 || InternalDictionary.ContainsKey(key));
    Contract.Ensures(!Contract.Result<bool>() || Count > 0);

    return InternalDictionary.ContainsKey(key);
}

Warning 5 Method 'My.Collections.Generic.ReadOnlyDictionary2.ContainsKey(type
parameter.TKey)' implements interface method
'System.Collections.Generic.IDictionary2.ContainsKey(type parameter.TKey)', thus cannot add Requires.

Answer 1

“我有一个自定义的字典包装器类”——它实现了 IDictionary<TKey, TValue> .接口(interface)方法可以指定契约，实现它们的类方法必须满足契约。在这种情况下，IDictionary<TKey, TValue>.ContainsKey(TKey)有您询问的契约(Contract):

Contract.Ensures(!Contract.Result<bool>() || this.Count > 0);

逻辑上，!a || b可以读作 a ===> b ( a 表示 b )，使用它，我们可以将其翻译成英文:

If ContainsKey() returns true, the dictionary must not be empty.

这是一个非常明智的要求。空字典不得声明包含键。 这是你需要证明的。

这是一个示例 DictionaryWrapper添加 Contract.Ensures 的类 promise Count的实现细节等于innerDictionary.Count是其他方法可以依赖的硬保证。它添加了一个类似的 Contract.Ensures至 ContainsKey这样 IDictionary<TKey, TValue>.TryGetValue契约(Contract)也是可验证的。

public class DictionaryWrapper<TKey, TValue> : IDictionary<TKey, TValue>
{
    IDictionary<TKey, TValue> innerDictionary;

    public DictionaryWrapper(IDictionary<TKey, TValue> innerDictionary)
    {
        Contract.Requires<ArgumentNullException>(innerDictionary != null);
        this.innerDictionary = innerDictionary;
    }

    [ContractInvariantMethod]
    private void Invariant()
    {
        Contract.Invariant(innerDictionary != null);
    }

    public void Add(TKey key, TValue value)
    {
        innerDictionary.Add(key, value);
    }

    public bool ContainsKey(TKey key)
    {
        Contract.Ensures(Contract.Result<bool>() == innerDictionary.ContainsKey(key));
        return innerDictionary.ContainsKey(key);
    }

    public ICollection<TKey> Keys
    {
        get
        {
            return innerDictionary.Keys;
        }
    }

    public bool Remove(TKey key)
    {
        return innerDictionary.Remove(key);
    }

    public bool TryGetValue(TKey key, out TValue value)
    {
        return innerDictionary.TryGetValue(key, out value);
    }

    public ICollection<TValue> Values
    {
        get
        {
            return innerDictionary.Values;
        }
    }

    public TValue this[TKey key]
    {
        get
        {
            return innerDictionary[key];
        }
        set
        {
            innerDictionary[key] = value;
        }
    }

    public void Add(KeyValuePair<TKey, TValue> item)
    {
        innerDictionary.Add(item);
    }

    public void Clear()
    {
        innerDictionary.Clear();
    }

    public bool Contains(KeyValuePair<TKey, TValue> item)
    {
        return innerDictionary.Contains(item);
    }

    public void CopyTo(KeyValuePair<TKey, TValue>[] array, int arrayIndex)
    {
        innerDictionary.CopyTo(array, arrayIndex);
    }

    public int Count
    {
        get
        {
            Contract.Ensures(Contract.Result<int>() == innerDictionary.Count);
            return innerDictionary.Count;
        }
    }

    public bool IsReadOnly
    {
        get
        {
            return innerDictionary.IsReadOnly;
        }
    }

    public bool Remove(KeyValuePair<TKey, TValue> item)
    {
        return innerDictionary.Remove(item);
    }

    public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator()
    {
        return innerDictionary.GetEnumerator();
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        return innerDictionary.GetEnumerator();
    }
}