// C# Eval Expression

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

​

// @nuget: Z.Expressions.Eval

​

/*

## Compile a C# expression from a context

​

All the `Compile` methods we learned in previous examples use the global `EvalContext`. You can learn more about why and when you should use an instance context in the [EvalContext](/eval-context) documentation.

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In this example, we will create an instance context, add a new extension method named `GreaterThan` and use the `Compile` method. Then after we will loop to show only item in our list that currently have a higher value than the current position in our loop.

​

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The method `GreaterThan` only exists for this context. That means the `Eval.Compile` is unaware and cannot use this method.

*/

​

using System;

using System.Collections.Generic;

using System.Diagnostics;

using Z.Expressions;

​

public class Program

{

    public static void Main()

    {

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

        var context = new EvalContext();

​

        context.AddMethod(@"

        bool GreaterThan(this int x, int y)

        {

            return x > y;

        }

        ");

        var compiled = context.Compile<Func<List<int>, int, List<int>>>("list.Where(x => x.GreaterThan(i))", "list", "i");  

        for(int i = 0; i < 4; i++)

        {

            var rList = compiled(list, i);

            FiddleHelper.WriteTable("i=" + i, rList);

        }       

    }

}