// C# Eval Expression

// Doc: https://eval-expression.net/register-unregister

​

// @nuget: Z.Expressions.Eval

​

/*

## RegisterGlobalVariable

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The RegisterGlobalVariable method registers a global variable value. This variable value is shared across all evaluations and can be modified.

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In this example, we will register a global variable. In the first expression, we will increment the value of the global variable and return it. In the second expression, we will return the value of the global variable and notice that it's the same value as the previous one since the variable is shared across all expressions. Lastly, we will check using `IsRegisteredGlobalVariable` and `UnregisterGlobalVariable` methods that the global variable was successfully registered and unregistered.

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> NOTE: A global variable has the same behavior as creating a static variable in the code, such as `public static int x = 1;`. The variable is readable and writable, so when changing the value, all codes accessing this variable also now have the modified value.

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See more: https://eval-expression.net/register-unregister

*/

​

using System;

using System.Collections.Generic;

using Z.Expressions;

​

public class Program

{

    public static void Main()

    {

        // Global Context: EvalManager.DefaultContext.RegisterKeyword("isin", "IsIn");

        var context = new EvalContext();

        context.RegisterExtensionMethod(typeof(CustomExtensions));;

        context.RegisterKeyword("isin", "IsIn");

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

        var r1 = context.Execute<bool>("2 isin list", new { list });

        Console.WriteLine("1 - Result: " + r1);

        // Check if the keyword "isin" is registered

        var r2 = context.IsRegisteredKeyword("isin"); // return true

        Console.WriteLine("2 - Result: " + r2);

        // Unregister the keyword "isin"

        context.UnregisterKeyword("isin");

        // Check if the keyword "isin" has been succesfully unregistered

        var r3 = context.IsRegisteredKeyword("isin"); // return false

        Console.WriteLine("3 - Result: " + r3);

    }

}

​

public static class CustomExtensions

{

    public static bool IsIn<T>(this T x, List<T> list)

    {

        return list.Contains(x);

    }

}