云南大王-表达式树
发布时间：2020-03-25 00:00:00
记录表达式树的学习过程
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> 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,
View Code
//
// 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(){ 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,
View Code
//
// 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,
View Code
（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,
View Code
Expression：BinaryExpression、IndexExpression、MethodCallExpression、UnaryExpression、BlockExpression、GotoExpression、DynamicExpression、LambdaExpression、MemberExpression等。
ExpressionVisitor。
