1、常量表达式树
Func<int> compile = (() => + );
使用表达式树的方式
ConstantExpression a = Expression.Constant();
ConstantExpression b = Expression.Constant();
BinaryExpression add = Expression.Add(a, b); Expression<Func<int>> lambda= Expression.Lambda<Func<int>>(add);
Func<int> compile2 = lambda.Compile();
调用
Console.WriteLine(compile());
Console.WriteLine(compile2());
输出结果
要点：
1、ConstantExpression 是常量表达式，通过Expression.Constant(object value)方法创建一个常量表达式
2、BinaryExpression 二元表达式 Expression.Add(Expression left,Expression right)这是加法二元表达式，同理还有Subtract、Multiply和Divide分别对应减、乘和除二元表达式
3、Expression.Lambda<Func<int>>(add)转换成lambda表达式树
4、lambda.Compile()将lambda表达式树转化成委托
2、参数表达式树
lambda表达式
Func<int, int> compile = x=>x+;
lambda表达式树
ConstantExpression a = Expression.Constant();
ParameterExpression b = Expression.Parameter(typeof(int),"b");
BinaryExpression add = Expression.Add(a, b); Expression<Func<int,int>> lambda= Expression.Lambda<Func<int,int>>(add,b);
Func<int,int> compile2 = lambda.Compile();
注意使用Expression.Lambda方法时，不需要提供常量表达式树
调用
Console.WriteLine(compile());
Console.WriteLine(compile2());
当left和right都是参数表达式树时
Func<int, int,int> compile = (x,y)=>x+y; ParameterExpression a = Expression.Parameter(typeof(int), "a");
ParameterExpression b = Expression.Parameter(typeof(int),"b");
BinaryExpression add = Expression.Add(a, b); Expression<Func<int,int,int>> lambda= Expression.Lambda<Func<int,int,int>>(add,a,b);
Func<int,int, int> compile2 = lambda.Compile(); Console.WriteLine(compile(,));
Console.WriteLine(compile2(,));