Lambda中Func和Expression的区别

Lambda中Func和Expression的区别

 

 

<span style="white-space:pre">    </span>static void TestExpression()
        {
            Func<int> Func = () => 10;
            Expression<Func<int>> Expression = () => 10;

            Func<int, bool> f = i => i == 10;
            Expression<Func<int, bool>> e = x => x == 10;


            //Func<TObject, bool> 是委托(delegate)
            //Expression < Func < TObject, bool >> 是表达式
            //Expression编译后就会变成delegate，才能运行。比如
            Expression<Func<int, bool>> ex = x => x < 10;
            Func<int, bool> func = ex.Compile();
            //然后你就可以调用func：
            func(5); //-返回 true
            func(20); //- 返回 false
            System.Console.WriteLine("func(5){0}", func(5));
            System.Console.WriteLine("func(20){0}", func(20));

            Func<int, bool> ff = i => i > 5;
            System.Console.WriteLine("ff(2){0}", ff(2));
            System.Console.WriteLine("ff(7){0}", ff(7));

        }

 

 

<span style="white-space:pre">    </span>static void TestExpression2()
        {
            Func<int> Func = () => 10;
            Expression<Func<int>> Expression = () => 10;

            Func<int, bool> f = i => i == 10;
            Expression<Func<int, bool>> e = x => x == 10;

            System.Console.WriteLine(Func);         //System.Func`1[System.Int32]
            System.Console.WriteLine(Func());       //10
            System.Console.WriteLine(f(5));         //false
            System.Console.WriteLine(f(10));        //true

            System.Console.WriteLine(Expression);           //() => 10;
            System.Console.WriteLine(Expression.Compile()); //System.Func`1[System.Int32]

            System.Console.WriteLine(e);            //x => (x == 10)
            System.Console.WriteLine(e.Compile());  //System.Func`2[System.Int32,System.Boolean]

            Func<int, bool> ff = e.Compile();
            System.Console.WriteLine(ff);            //System.Func`2[System.Int32,System.Boolean]
            System.Console.WriteLine(ff(5));         //false
            System.Console.WriteLine(ff(10));        //true



            Func<int> fff = Expression.Compile();
            System.Console.WriteLine(fff);      //System.Func`1[System.Int32]
            System.Console.WriteLine(fff());    //10
        }