// C# Eval Expression

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

​

// @nuget: Z.Expressions.Eval

​

/*

## Evaluate a C# expression from a context

​

All the `Execute` methods we learned in previous examples use the global EvalContext stored in the EvalManager.DefaultContext. In other words:

​

- using the `Eval.Execute` method is similar to doing `EvalManager.DefaultContext.Execute`.

- using the `"the_string_expression".Execute` method is similar to doing `EvalManager.DefaultContext.Execute`.

​

So anyway, what exactly is an EvalContext? That is a class you instancies to set options specific to the current context that you do not want to apply globally to all your evaluation.

​

For example, you would like to run an expression in safe mode, specify some global variables, or even use the `AddMethod`.

​

In this example, we will create an instance context, add a new extension method named `GreaterThan` and use the `Execute` method.

​

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

​

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

*/

​

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;

        var context = new EvalContext();

        context.AddMethod(@"

bool GreaterThan(this int x, int y)

{

    return x > y;

}

");

        list = context.Execute<List<int>>("list.Where(x => x.GreaterThan(greaterThan))", new { list, greaterThan }); 

        FiddleHelper.WriteTable(list);

    }

}