C# Contract诊断

命名空间 : using System.Diagnostics.Contracts;

属性标记 : [ContractOption(category: "runtime", setting: "checking", enabled: true)]

事件订阅 : Contract.ContractFailed += (sender, e) => {  Console.WriteLine(e.Message);  };

1、 Requires() 定义前提条件

 static void MinMax(int min,int max)
         {
             Contract.Requires(min <= max);
             Contract.Requires <ArgumentException>(min <= max);
         }
         static void Preconditions(object o)
         {
             Contract.Requires<ArgumentNullException>(o != null, "Preconditions, o may not be null");
             Console.WriteLine(o.GetType().Name);
         }
         static void ArrayTest(int [] data)
         {
             Contract.Requires(Contract.ForAll(data, i => i < ));
             Console.WriteLine("ArrayTest contract succeeded");
         }
         public void ArrayTestWithPureMethod(int [] data)
         {
             Contract.Requires(Contract.ForAll(data, MyDataCheck));
             Console.WriteLine("ArrayWithPureMethod succeeded");
         }

         public int MaxVal { get; set; }
         public bool MyDataCheck(int x)
         {
             return x <= MaxVal;
         }

2、  Ensures() 定义后置条件

   private static int sharedState = ;

         static void Postcondition()
         {
             Contract.Ensures(sharedState < );
             sharedState = ;
             Console.WriteLine("change sharedState invariant {0}", sharedState);
             sharedState = ;
             Console.WriteLine("before returning change it to a valid value {0}", sharedState);
         }

         static int ReturnValue()
         {
             Contract.Ensures(Contract.Result<int>() < );
             return ;
         }
         static int ReturnLargerThanInput(int x)
         {
             Contract.Ensures(Contract.Result<int>() > Contract.OldValue<int>(x));
             return x+;
         }
         static void OutParameters(out int x, out int y)
         {
             Contract.Ensures(Contract.ValueAtReturn<int>(out x) >  && Contract.ValueAtReturn<int>(out x) < );
             Contract.Ensures(Contract.ValueAtReturn<int>(out y) %  == );
             x = ;
             y = ;
         }

3、  Invariant() 定义在对象的整个生命周期中都必须满足的条件

   private int x = ;
         [ContractInvariantMethod]
         private void ObjectInvariant()
         {
             Contract.Invariant(x > );
         }

         public void Invariant()
         {
             x = ;
             Console.WriteLine("invariant value: {0}", x);
         }

4、  Pure特性，可以把方法和类型标记为纯粹的方法，纯粹指的是自定义方法不会修改对象的任何可见状态。

5、  接口协定

 [ContractClass(typeof(PersonContract))]
    public  interface IPerson
     {
        string FirstName{get;set;}
        string LastName { get; set; }
        int Age { get; set; }
        void ChangeName(string firstName, string lastName);
     }

  [ContractClassFor(typeof(IPerson))]
    public abstract class PersonContract:IPerson
     {
          string IPerson.FirstName
         {
             get
             {
                 return Contract.Result<string>();
             }
             set
             {
                 Contract.Requires(value != null);
             }
         }

          string IPerson.LastName
         {
             get
             {
                 return Contract.Result<string>();
             }
             set
             {
                 Contract.Requires(value != null);
             }
         }

          int IPerson.Age
         {
             get
             {
                 Contract.Ensures(Contract.Result<int>() >=  && Contract.Result<int>() < );
                 return Contract.Result<int>();
             }
             set
             {
                 Contract.Requires(value >=  && value < );
             }
         }

           void IPerson.ChangeName(string firstName, string lastName)
         {
             Contract.Requires(firstName != null);
             Contract.Requires(lastName != null);
         }
     }

  public  class Person:IPerson
     {
       public Person() { }
       public Person(string firstName,string lastName)
       {
           this.FirstName = firstName;
           this.LastName = lastName;
       }
         public string FirstName
         {
             get ;
              set;

         }

         public string LastName
         {
             get;
              set;
         }

         public int Age
         {
             get;
              set;
         }

         public void ChangeName(string firstName, string lastName)
         {
             this.FirstName = firstName;
             this.LastName = lastName;
         }
     }