表达式树

记录的学习过程

表达式树将代码表示为可以检测、修改、或执行的一种结构，一种定义代码的结构。

表达式树是代码的完整表示形式：可以看到任何子表达式的值。 可以看到方法和属性名称。 可以看到任何常数表达式的值。 还可以将自己转换为可执行的委托，并执行代码。

通过表达式树 api，可创建几乎任何有效代码构造的树。 但不能在表达式树中创建某些 c# 习惯用语，第一 异步的async、await，第二是循环（循环有什么习惯用语？我凌乱了）。

 表达式树是不可变的数据结构， 只能换新树。

 

访问表达式树变量

 public static void main()
 {            
     expression<func<int, int>> addfive = num => num + 5;
     // expressiontype有add、addchecked、and、andalso、divide、equal、lambda、multiply等。
     if (addfive.nodetype== expressiontype.lambda)
     {
         var lambdaexp = (lambdaexpression)addfive;
         var parameter = lambdaexp.parameters.first();
         console.writeline(parameter.name);
         console.writeline(parameter.type);

         console.writeline(lambdaexp.parameters.last().name); //跟上面同一个
         console.writeline(lambdaexp.parameters.last().type);                
     }
 }

创建表达式树

public static void main()
{           
    // 常量表达式树
    constantexpression one = expression.constant(1, typeof(int));
    constantexpression two = expression.constant(2, typeof(int));
    // 二进制表达式树
    binaryexpression addition = expression.add(one, two);
}

 

表达式树api

expressiontype:（convertchecked 和convert明明c#写法一样，怎么表达不同节点类型，迷茫... multiply和multiplychecked，迷茫...，newarraybounds 多维数组）

//
// 摘要:
//     an addition operation, such as a + b, without overflow checking, for numeric
//     operands.
add = 0,
//
// 摘要:
//     an addition operation, such as (a + b), with overflow checking, for numeric operands.
addchecked = 1,
//
// 摘要:
//     a bitwise or logical and operation, such as (a & b) in c# and (a and b) in visual
//     basic.
and = 2,
//
// 摘要:
//     a conditional and operation that evaluates the second operand only if the first
//     operand evaluates to true. it corresponds to (a && b) in c# and (a andalso b)
//     in visual basic.
andalso = 3,
//
// 摘要:
//     an operation that obtains the length of a one-dimensional array, such as array.length.
arraylength = 4,
//
// 摘要:
//     an indexing operation in a one-dimensional array, such as array[index] in c#
//     or array(index) in visual basic.
arrayindex = 5,
//
// 摘要:
//     a method call, such as in the obj.samplemethod() expression.
call = 6,
//
// 摘要:
//     a node that represents a null coalescing operation, such as (a ?? b) in c# or
//     if(a, b) in visual basic.
coalesce = 7,
//
// 摘要:
//     a conditional operation, such as a > b ? a : b in c# or if(a > b, a, b) in visual
//     basic.
conditional = 8,
//
// 摘要:
//     a constant value.
constant = 9,
//
// 摘要:
//     a cast or conversion operation, such as (sampletype)obj in c#or ctype(obj, sampletype)
//     in visual basic. for a numeric conversion, if the converted value is too large
//     for the destination type, no exception is thrown.
convert = 10,
//
// 摘要:
//     a cast or conversion operation, such as (sampletype)obj in c#or ctype(obj, sampletype)
//     in visual basic. for a numeric conversion, if the converted value does not fit
//     the destination type, an exception is thrown.
convertchecked = 11,

//
// 摘要:
//     a division operation, such as (a / b), for numeric operands.
divide = 12,
//
// 摘要:
//     a node that represents an equality comparison, such as (a == b) in c# or (a =
//     b) in visual basic.
equal = 13,
//
// 摘要:
//     a bitwise or logical xor operation, such as (a ^ b) in c# or (a xor b) in visual
//     basic.
exclusiveor = 14,
//
// 摘要:
//     a "greater than" comparison, such as (a > b).
greaterthan = 15,
//
// 摘要:
//     a "greater than or equal to" comparison, such as (a >= b).
greaterthanorequal = 16,
//
// 摘要:
//     an operation that invokes a delegate or lambda expression, such as sampledelegate.invoke().
invoke = 17,
//
// 摘要:
//     a lambda expression, such as a => a + a in c# or function(a) a + a in visual
//     basic.
lambda = 18,
//
// 摘要:
//     a bitwise left-shift operation, such as (a << b).
leftshift = 19,
//
// 摘要:
//     a "less than" comparison, such as (a < b).
lessthan = 20,
//
// 摘要:
//     a "less than or equal to" comparison, such as (a <= b).
lessthanorequal = 21,
//
// 摘要:
//     an operation that creates a new system.collections.ienumerable object and initializes
//     it from a list of elements, such as new list<sampletype>(){ a, b, c } in c# or
//     dim samplelist = { a, b, c } in visual basic.
listinit = 22,
//
// 摘要:
//     an operation that reads from a field or property, such as obj.sampleproperty.
memberaccess = 23,
//
// 摘要:
//     an operation that creates a new object and initializes one or more of its members,
//     such as new point { x = 1, y = 2 } in c# or new point with {.x = 1, .y = 2} in
//     visual basic.
memberinit = 24,

 //
        // 摘要:
        //     an arithmetic remainder operation, such as (a % b) in c# or (a mod b) in visual
        //     basic.
        modulo = 25,
        //
        // 摘要:
        //     a multiplication operation, such as (a * b), without overflow checking, for numeric
        //     operands.
        multiply = 26,
        //
        // 摘要:
        //     an multiplication operation, such as (a * b), that has overflow checking, for
        //     numeric operands.
        multiplychecked = 27,
        //
        // 摘要:
        //     an arithmetic negation operation, such as (-a). the object a should not be modified
        //     in place.
        negate = 28,
        //
        // 摘要:
        //     a unary plus operation, such as (+a). the result of a predefined unary plus operation
        //     is the value of the operand, but user-defined implementations might have unusual
        //     results.
        unaryplus = 29,
        //
        // 摘要:
        //     an arithmetic negation operation, such as (-a), that has overflow checking. the
        //     object a should not be modified in place.
        negatechecked = 30,
        //
        // 摘要:
        //     an operation that calls a constructor to create a new object, such as new sampletype().
        new = 31,
        //
        // 摘要:
        //     an operation that creates a new one-dimensional array and initializes it from
        //     a list of elements, such as new sampletype[]{a, b, c} in c# or new sampletype(){a,
        //     b, c} in visual basic.
        newarrayinit = 32,
        //
        // 摘要:
        //     an operation that creates a new array, in which the bounds for each dimension
        //     are specified, such as new sampletype[dim1, dim2] in c# or new sampletype(dim1,
        //     dim2) in visual basic.
        newarraybounds = 33,
        //
        // 摘要:
        //     a bitwise complement or logical negation operation. in c#, it is equivalent to
        //     (~a) for integral types and to (!a) for boolean values. in visual basic, it is
        //     equivalent to (not a). the object a should not be modified in place.
        not = 34,

（quote节点类型是什么？）

 //
        // 摘要:
        //     a bitwise complement or logical negation operation. in c#, it is equivalent to
        //     (~a) for integral types and to (!a) for boolean values. in visual basic, it is
        //     equivalent to (not a). the object a should not be modified in place.
        not = 34,
        //
        // 摘要:
        //     an inequality comparison, such as (a != b) in c# or (a <> b) in visual basic.
        notequal = 35,
        //
        // 摘要:
        //     a bitwise or logical or operation, such as (a | b) in c# or (a or b) in visual
        //     basic.
        or = 36,
        //
        // 摘要:
        //     a short-circuiting conditional or operation, such as (a || b) in c# or (a orelse
        //     b) in visual basic.
        orelse = 37,
        //
        // 摘要:
        //     a reference to a parameter or variable that is defined in the context of the
        //     expression. for more information, see system.linq.expressions.parameterexpression.
        parameter = 38,
        //
        // 摘要:
        //     a mathematical operation that raises a number to a power, such as (a ^ b) in
        //     visual basic.
        power = 39,
        //
        // 摘要:
        //     an expression that has a constant value of type system.linq.expressions.expression.
        //     a system.linq.expressions.expressiontype.quote node can contain references to
        //     parameters that are defined in the context of the expression it represents.
        quote = 40,
        //
        // 摘要:
        //     a bitwise right-shift operation, such as (a >> b).
        rightshift = 41,

 expression：binaryexpression、indexexpression、methodcallexpression、unaryexpression、blockexpression、gotoexpression、dynamicexpression、lambdaexpression、memberexpression等。

expressionvisitor。