Expression trees represent code in a tree-like data structure, where each node is an expression, for example, a method call or a binary operation such as x < y.
You can compile and run code represented by expression trees. This enables dynamic modification of executable code, the execution of LINQ queries in various databases, and the creation of dynamic queries.
Expression trees are also used in the dynamic language runtime (DLR) to provide interoperability between dynamic languages and .NET and to enable compiler writers to emit expression trees instead of Microsoft intermediate language (MSIL).
A language is homoiconic if a program written in it can be manipulated as data using the language, and thus the program's internal representation can be inferred just by reading the program itself. This property is often summarized by saying that the language treats code as data. - Wiki
Expression<Func<int, bool>> isNegativeExp = i => i < 0;
Console.WriteLine(isNegativeExp.Body);
/*
* Type: Func<int, bool>
* Expression: i < 0
* Lambda Operator: =>
* Parameter: Left of =>
* Body Expression: Right of =>
* Lambda Expression: i => i < 0
*/- Left Expression -> NodeType (Equal, NotEqual, etc.) -> Right Expression
- Traverses any expression tree, allowing us to view a current node or provided node in it's place
- Read each piece of the expression and operates
Expression<Func<int, bool>> lambda = num => num < 5;
ParameterExpression numParam = Expression.Parameter(typeof(int), "num");
ConstantExpression five = Expression.Constant(5, typeof(int));
BinaryExpression numLessThanFive = Expression.LessThan(numParam, five);
Expression<Func<int, bool>> lambda1 =
Expression.Lambda<Func<int, bool>>(
numLessThanFive,
new ParameterExpression[] { numParam }); flowchart LR;
style A fill:#008080,stroke:#fff,stroke-width:1px,color:#fff
style B fill:#006666,stroke:#fff,stroke-width:1px,color:#fff
style C fill:#004c4c,stroke:#fff,stroke-width:1px,color:#fff
A(C# Code)-- Compiler -->B(MSIL Code);
B-- JIT -->C(Native Code);