// C# Eval Expression

// Doc: https://eval-expression.net/my-first-compilation

​

// @nuget: Z.Expressions.Eval

​

/*

## Compile a C# expression with variable names

​

With the 2 previous topics, you should now be able to compile an expression and understand how to return the type of the compiled method.

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However, almost every time, the compiled method would also have parameters.

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There are multiple ways to pass variable names, such as:

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- Position

- Named variables

- ExpandoObject

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In the following example, we will see all the different ways to pass variable names that will be used in our expression to compile.

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See more: https://eval-expression.net/my-first-compilation

*/

​

using System;

using System.Dynamic;

using System.Collections.Generic;

using Z.Expressions;

​

public class Program

{

    public static void Main()

    {

        var list = new List<int>() { 1, 2, 3, 4 };

        var greaterThan = 2;

        // Passing parameters with position

        // NOTE: In this example, {0} is the first `List<int>` and {1} is the `int`

        {

            var compiled = Eval.Compile<Func<List<int>, int, List<int>>>("{0}.Where(x => x > {1})");

            var rList = compiled(list, greaterThan);

            FiddleHelper.WriteTable((IEnumerable<int>)rList);

        }

        // Passing parameters with named variables

        // NOTE: You need to name as many variables as the `Func` have (without counting the return type)

        {

            var compiled = Eval.Compile<Func<List<int>, int, List<int>>>("list.Where(x => x > greaterThan)", "list", "greaterThan");

            var rList = compiled(list, greaterThan);

            FiddleHelper.WriteTable((IEnumerable<int>)rList);

        }

        // Passing parameters with an ExpandoObject

        // NOTE: More flexible than the 2 previous examples but less robust as the library assume any missing name is part of the ExpandoObject

        // NOTE: We had to cast the list to `(List<int>)` as until the method is executed, the library doesn't know which type is the variable `list`

        {

            dynamic expandoObject = new ExpandoObject();

            expandoObject.list = list;

            expandoObject.greaterThan= greaterThan;

            var compiled = Eval.Compile<Func<ExpandoObject, List<int>>>("((List<int>)list).Where(x => x > greaterThan)");

            var rList = compiled(expandoObject);

            FiddleHelper.WriteTable((IEnumerable<int>)rList);

        }

    }

}