C#五类运算符使用表达式树进行操作

在 C# 中，算术运算符，有以下类型

• 算术运算符
• 关系运算符
• 逻辑运算符
• 位运算符
• 赋值运算符
• 其他运算符

这些运算符根据参数的多少，可以分作一元运算符、二元运算符、三元运算符。本文将围绕这些运算符，演示如何使用表达式树进行操作。

对于一元运算符和二元运算符的 Expression 的子类型如下：

UnaryExpression; //一元运算表达式
BinaryExpression; //二元运算表达式

一，算术运算符

+ 与 Add()

正常代码

            int a;
            int b;
            a = 100;
            b = 200;
            var ab = a + b;
            Console.WriteLine(ab);

使用表达式树构建

            ParameterExpression a = Expression.Parameter(typeof(int), "a");
            ParameterExpression b = Expression.Parameter(typeof(int), "b");

            // ab = a + b
            BinaryExpression ab = Expression.Add(a, b);

            // 打印 a + b 的值
            MethodCallExpression method = Expression.Call(null, typeof(Console).GetMethod("WriteLine", new Type[] { typeof(int) }), ab);

            Expression<Action<int, int>> lambda = Expression.Lambda<Action<int, int>>(method, a, b);
            lambda.Compile()(100, 200);

            Console.ReadKey();

如果想复杂一些，使用 块 来执行：

            ParameterExpression a = Expression.Parameter(typeof(int), "a");
            ParameterExpression b = Expression.Parameter(typeof(int), "b");

            // 别忘记了赋值
            BinaryExpression aa = Expression.Assign(a, Expression.Constant(100, typeof(int)));
            BinaryExpression bb = Expression.Assign(b, Expression.Constant(200, typeof(int)));

            // ab = a + b
            BinaryExpression ab = Expression.Add(a, b);

            // 打印 a + b 的值
            MethodCallExpression method = Expression.Call(null, typeof(Console).GetMethod("WriteLine", new Type[] { typeof(int) }), ab);

            // 以块的形式执行代码，相当于{ }
            // 不需要纠结这里，后面会有详细说明，重点是上面
            var call = Expression.Block(new ParameterExpression[] { a, b }, aa, bb, method);
            Expression<Action> lambda = Expression.Lambda<Action>(call);
            lambda.Compile()();

上面两个示例，是使用表达式树计算结果，然后还是使用表达式树打印结果。

前者依赖外界传入参数值，赋予 a、b，后者则全部使用表达式树赋值和运算。

那么，如何通过表达式树执行运算，获取执行结果呢？

            ParameterExpression a = Expression.Parameter(typeof(int), "a");
            ParameterExpression b = Expression.Parameter(typeof(int), "b");

            // ab = a + b
            BinaryExpression ab = Expression.Add(a, b);

            Expression<Func<int, int, int>> lambda = Expression.Lambda<Func<int, int, int>>(ab, a, b);
            int result = lambda.Compile()(100, 200);

            Console.WriteLine(result);
            Console.ReadKey();

这些区别在于如何编写 Expression.Lambda()。

另外，使用 AddChecked() 可以检查操作溢出。

- 与 Subtract()

与加法一致，此处不再赘述，SubtractChecked() 可以检查溢出。

a - b ，结果是 100 。

            ParameterExpression a = Expression.Parameter(typeof(int), "a");
            ParameterExpression b = Expression.Parameter(typeof(int), "b");

            // ab = a - b
            BinaryExpression ab = Expression.Subtract(a, b);

            Expression<Func<int, int, int>> lambda = Expression.Lambda<Func<int, int, int>>(ab, a, b);
            int result = lambda.Compile()(200, 100);

            Console.WriteLine(result);

乘除、取模

乘法

            // ab = a * b
            BinaryExpression ab = Expression.Multiply(a, b);
// ab = 20000

除法

            // ab = a / b
            BinaryExpression ab = Expression.Divide(a, b);
// ab = 2

取模(%)

            ParameterExpression a = Expression.Parameter(typeof(int), "a");
            ParameterExpression b = Expression.Parameter(typeof(int), "b");

            // ab = a % b
            BinaryExpression ab = Expression.Modulo(a, b);

            Expression<Func<int, int, int>> lambda = Expression.Lambda<Func<int, int, int>>(ab, a, b);
            int result = lambda.Compile()(200, 150);
// ab = 50
            Console.WriteLine(result);
            Console.ReadKey();

自增自减

自增自减有两种模型，一种是 x++ 或 x--，另一种是 ++x 或 --x。

他们都是属于 UnaryExpression 类型。

巧记：Post 后置， Pre 前置；Increment 是加，Decrement是减；Assign与赋值有关(后面会说到)；

x++ 与 x-- 的使用

            int a = 10;
            int b = 10;
            a++;
            b--;
            Console.WriteLine(a);
            Console.WriteLine(b);

            // int a,b;
            ParameterExpression a = Expression.Parameter(typeof(int), "a");
            ParameterExpression b = Expression.Parameter(typeof(int), "b");

            // a = 10,b = 10;
            BinaryExpression setA = Expression.Assign(a, Expression.Constant(10));
            BinaryExpression setB = Expression.Assign(b, Expression.Constant(10));

            // a++
            UnaryExpression aa = Expression.PostIncrementAssign(a);

            // b--
            UnaryExpression bb = Expression.PostDecrementAssign(b);

            //Console.WriteLine(a);
            //Console.WriteLine(b);
            MethodCallExpression callA = Expression.Call(null, typeof(Console).GetMethod("WriteLine", new Type[] { typeof(int) }), a);
            MethodCallExpression callB = Expression.Call(null, typeof(Console).GetMethod("WriteLine", new Type[] { typeof(int) }), b);

            BlockExpression block = Expression.Block(
                new ParameterExpression[] { a, b },
                setA,
                setB,
                aa,
                bb,
                callA,
                callB
                );

            Expression<Action> lambda = Expression.Lambda<Action>(block);
            lambda.Compile()();

            Console.ReadKey();

如果想把参数从外面传入，设置 a，b

            // int a,b;
            ParameterExpression a = Expression.Variable(typeof(int), "a");
            ParameterExpression b = Expression.Variable(typeof(int), "b");

            // a++
            UnaryExpression aa = Expression.PostIncrementAssign(a);

            // b--
            UnaryExpression bb = Expression.PostDecrementAssign(b);

            //Console.WriteLine(a);
            //Console.WriteLine(b);
            MethodCallExpression callA = Expression.Call(null, typeof(Console).GetMethod("WriteLine", new Type[] { typeof(int) }), a);
            MethodCallExpression callB = Expression.Call(null, typeof(Console).GetMethod("WriteLine", new Type[] { typeof(int) }), b);

            BlockExpression block = Expression.Block(
                aa,
                bb,
                callA,
                callB
                );

            Expression<Action<int, int>> lambda = Expression.Lambda<Action<int, int>>(block, a, b);
            lambda.Compile()(10, 10);
            Console.ReadKey();

生成的表达式树如下

.Lambda #Lambda1<System.Action`2[System.Int32,System.Int32]>(
    System.Int32 $a,
    System.Int32 $b) {
    .Block() {
        $a++;
        $b--;
        .Call System.Console.WriteLine($a);
        .Call System.Console.WriteLine($b)
    }
}

为了理解一下 Expression.Block()，可以在这里学习一下(后面会说到 Block())。

            // int a,b;
            ParameterExpression a = Expression.Parameter(typeof(int), "a");
            ParameterExpression b = Expression.Parameter(typeof(int), "b");
            ParameterExpression c = Expression.Variable(typeof(int), "c");

            BinaryExpression SetA = Expression.Assign(a, c);
            BinaryExpression SetB = Expression.Assign(b, c);
            // a++
            UnaryExpression aa = Expression.PostIncrementAssign(a);

            // b--
            UnaryExpression bb = Expression.PostDecrementAssign(b);

            //Console.WriteLine(a);
            //Console.WriteLine(b);
            MethodCallExpression callA = Expression.Call(null, typeof(Console).GetMethod("WriteLine", new Type[] { typeof(int) }), a);
            MethodCallExpression callB = Expression.Call(null, typeof(Console).GetMethod("WriteLine", new Type[] { typeof(int) }), b);

            BlockExpression block = Expression.Block(
                new ParameterExpression[] { a, b },
                SetA,
                SetB,
                aa,
                bb,
                callA,
                callB
                );

            Expression<Action<int>> lambda = Expression.Lambda<Action<int>>(block, c);
            lambda.Compile()(10);

            Console.ReadKey();

为什么这里要多加一个 c 呢？我们来看看生成的表达式树

.Lambda #Lambda1<System.Action`1[System.Int32]>(System.Int32 $c) {
    .Block(
        System.Int32 $a,
        System.Int32 $b) {
        $a = $c;
        $b = $c;
        $a++;
        $b--;
        .Call System.Console.WriteLine($a);
        .Call System.Console.WriteLine($b)
    }
}

观察一下下面代码生成的表达式树

            // int a,b;
            ParameterExpression a = Expression.Parameter(typeof(int), "a");
            ParameterExpression b = Expression.Parameter(typeof(int), "b");

            // a++
            UnaryExpression aa = Expression.PostIncrementAssign(a);

            // b--
            UnaryExpression bb = Expression.PostDecrementAssign(b);

            //Console.WriteLine(a);
            //Console.WriteLine(b);
            MethodCallExpression callA = Expression.Call(null, typeof(Console).GetMethod("WriteLine", new Type[] { typeof(int) }), a);
            MethodCallExpression callB = Expression.Call(null, typeof(Console).GetMethod("WriteLine", new Type[] { typeof(int) }), b);

            BlockExpression block = Expression.Block(
                new ParameterExpression[] { a, b },
                aa,
                bb,
                callA,
                callB
                );

            Expression<Action<int, int>> lambda = Expression.Lambda<Action<int, int>>(block, a, b);
            lambda.Compile()(10, 10);
            Console.ReadKey();

.Lambda #Lambda1<System.Action`2[System.Int32,System.Int32]>(
    System.Int32 $a,
    System.Int32 $b) {
    .Block(
        System.Int32 $a,
        System.Int32 $b) {
        $a++;
        $b--;
        .Call System.Console.WriteLine($a);
        .Call System.Console.WriteLine($b)
    }
}

关于前置的自增自减，按照上面示例编写即可，但是需要注意的是， ++x 和 --x ，是“先运算后增/自减”。

二，关系运算符

==、!=、>、<、>=、<=

C# 中的关系运算符如下

== 表示相等比较，如果是值类型和 string 类型，则比较值是否相同；如果是引用类型，则比较引用的地址是否相等。

其它的关系运算符则是仅比较值类型的大小。

实例代码

            int a = 21;
            int b = 10;
            Console.Write("a == b：");
            Console.WriteLine(a == b);

            Console.Write("a < b ：");
            Console.WriteLine(a < b);

            Console.Write("a > b ：");
            Console.WriteLine(a > b);

            // 改变 a 和 b 的值
            a = 5;
            b = 20;

            Console.Write("a <= b：");
            Console.WriteLine(a <= b);

            Console.Write("a >= b：");
            Console.WriteLine(b >= a);

            Console.ReadKey();

使用表达式树实现

            // int a,b;
            ParameterExpression a = Expression.Parameter(typeof(int), "a");
            ParameterExpression b = Expression.Parameter(typeof(int), "b");

            // a = 21,b = 10;
            BinaryExpression setA = Expression.Assign(a, Expression.Constant(21));
            BinaryExpression setB = Expression.Assign(b, Expression.Constant(20));

            // Console.Write("a == b：");
            // Console.WriteLine(a == b);
            MethodCallExpression call1 = Expression.Call(null,
                typeof(Console).GetMethod("Write", new Type[] { typeof(string) }),
                Expression.Constant("a == b："));
            MethodCallExpression call11 = Expression.Call(null,
                typeof(Console).GetMethod("WriteLine", new Type[] { typeof(bool) }),
                Expression.Equal(a, b));

            // Console.Write("a < b ：");
            // Console.WriteLine(a < b);
            MethodCallExpression call2 = Expression.Call(null,
                typeof(Console).GetMethod("Write", new Type[] { typeof(string) }),
                Expression.Constant("a < b ："));
            MethodCallExpression call22 = Expression.Call(null,
                typeof(Console).GetMethod("WriteLine", new Type[] { typeof(bool) }),
                Expression.LessThan(a, b));

            // Console.Write("a > b ：");
            // Console.WriteLine(a > b);
            MethodCallExpression call3 = Expression.Call(null,
                typeof(Console).GetMethod("Write", new Type[] { typeof(string) }),
                Expression.Constant("a > b ："));
            MethodCallExpression call33 = Expression.Call(null,
                typeof(Console).GetMethod("WriteLine", new Type[] { typeof(bool) }),
                Expression.GreaterThan(a, b));

            // 改变 a 和 b 的值
            // a = 5;
            // b = 20;
            BinaryExpression setAa = Expression.Assign(a, Expression.Constant(5));
            BinaryExpression setBb = Expression.Assign(b, Expression.Constant(20));

            // Console.Write("a <= b：");
            // Console.WriteLine(a <= b);
            MethodCallExpression call4 = Expression.Call(null,
                typeof(Console).GetMethod("Write", new Type[] { typeof(string) }),
                Expression.Constant("a <= b："));
            MethodCallExpression call44 = Expression.Call(null,
                typeof(Console).GetMethod("WriteLine", new Type[] { typeof(bool) }),
                Expression.LessThanOrEqual(a, b));

            // Console.Write("a >= b：");
            // Console.WriteLine(b >= a);
            MethodCallExpression call5 = Expression.Call(null,
                typeof(Console).GetMethod("Write", new Type[] { typeof(string) }),
                Expression.Constant("a >= b："));
            MethodCallExpression call55 = Expression.Call(null,
                typeof(Console).GetMethod("WriteLine", new Type[] { typeof(bool) }),
                Expression.GreaterThanOrEqual(a, b));

            BlockExpression block = Expression.Block(new ParameterExpression[] { a, b },
                setA,
                setB,
                call1,
                call11,
                call2,
                call22,
                call3,
                call33,
                setAa,
                setBb,
                call4,
                call44,
                call5,
                call55
                );

            Expression<Action> lambda = Expression.Lambda<Action>(block);
            lambda.Compile()();
            Console.ReadKey();

生成的表达式树如下

.Lambda #Lambda1<System.Action>() {
    .Block(
        System.Int32 $a,
        System.Int32 $b) {
        $a = 21;
        $b = 20;
        .Call System.Console.Write("a == b：");
        .Call System.Console.WriteLine($a == $b);
        .Call System.Console.Write("a < b ：");
        .Call System.Console.WriteLine($a < $b);
        .Call System.Console.Write("a > b ：");
        .Call System.Console.WriteLine($a > $b);
        $a = 5;
        $b = 20;
        .Call System.Console.Write("a <= b：");
        .Call System.Console.WriteLine($a <= $b);
        .Call System.Console.Write("a >= b：");
        .Call System.Console.WriteLine($a >= $b)
    }
}

三，逻辑运算符

&&、||、!

逻辑运算符的运行，结果是 true 或 false。

            int a = 10;
            int b = 11;

            Console.Write("[a == b && a > b]：");
            Console.WriteLine(a == b && a > b);

            Console.Write("[a > b || a == b]：");
            Console.WriteLine(a > b || a == b);

            Console.Write("[!(a == b)]：");
            Console.WriteLine(!(a == b));
            Console.ReadKey();

使用表达式树编写

            //int a = 10;
            //int b = 11;
            ParameterExpression a = Expression.Parameter(typeof(int), "a");
            ParameterExpression b = Expression.Parameter(typeof(int), "b");
            BinaryExpression setA = Expression.Assign(a, Expression.Constant(10));
            BinaryExpression setB = Expression.Assign(b, Expression.Constant(11));

            //Console.Write("[a == b && a > b]：");
            //Console.WriteLine(a == b && a > b);
            MethodCallExpression call1 = Expression.Call(null, typeof(Console).GetMethod("Write", new Type[] { typeof(string) }), Expression.Constant("[a == b && a > b]："));

            MethodCallExpression call2 = Expression.Call(
                null,
                typeof(Console).GetMethod("WriteLine", new Type[] { typeof(bool) }),
                 Expression.AndAlso(Expression.Equal(a, b), Expression.GreaterThan(a, b))
                );

            //Console.Write("[a > b || a == b]：");
            //Console.WriteLine(a > b || a == b);
            MethodCallExpression call3 = Expression.Call(null, typeof(Console).GetMethod("Write", new Type[] { typeof(string) }), Expression.Constant("[a > b || a == b]："));
            MethodCallExpression call4 = Expression.Call(
                null,
                typeof(Console).GetMethod("WriteLine", new Type[] { typeof(bool) }),
                Expression.OrElse(Expression.Equal(a, b), Expression.GreaterThan(a, b))
                );

            //Console.Write("[!(a == b)]：");
            //Console.WriteLine(!(a == b));
            MethodCallExpression call5 = Expression.Call(null, typeof(Console).GetMethod("Write", new Type[] { typeof(string) }), Expression.Constant("[!(a == b)]："));
            MethodCallExpression call6 = Expression.Call(
                null,
                typeof(Console).GetMethod("WriteLine", new Type[] { typeof(bool) }),
                Expression.Not(Expression.Equal(a, b))
                );
            BlockExpression block = Expression.Block(
                new ParameterExpression[] { a, b },
                setA,
                setB,
                call1,
                call2,
                call3,
                call4,
                call5,
                call6
                );

            Expression<Action> lambda = Expression.Lambda<Action>(block);
            lambda.Compile()();
            Console.ReadKey();

生成的表达式树如下

.Lambda #Lambda1<System.Action>() {
    .Block(
        System.Int32 $a,
        System.Int32 $b) {
        $a = 10;
        $b = 11;
        .Call System.Console.Write("[a == b && a > b]：");
        .Call System.Console.WriteLine($a == $b && $a > $b);
        .Call System.Console.Write("[a > b || a == b]：");
        .Call System.Console.WriteLine($a == $b || $a > $b);
        .Call System.Console.Write("[!(a == b)]：");
        .Call System.Console.WriteLine(!($a == $b))
    }
}

四，位运算符

&、|、^、~、<<、>>

限于篇幅，就写示例了。

五，赋值运算符

限于篇幅,请自行领略... ...

^= ，注意有两种意思一种是位运算符的异或(ExclusiveOrAssign)，一种是算术运算符的幂运算(PowerAssign)。

六，其他运算符

到此这篇关于C#五类运算符使用表达式树进行操作的文章就介绍到这了。希望对大家的学习有所帮助，也希望大家多多支持我们。