// C# Eval Expression

// Doc: https://eval-expression.net/options

​

// @nuget: Z.Expressions.Eval

​

/*

## VariableFactory

​

The VariableFactory option lets you get or sets a factory to return a value when a variable is not found. In other words, it allows specifying a value for a variable on demand. By default, the VariableFactory value is `null`.

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In this example, we will first execute a simple expression `X + 2` without specifying any value for `X`, which will fail. Then we will set the `VariableFactory` option to specify how to handle missing variables. In our case, we will set `1` as the value for `X` and specify that the missing variable name has been handled in this case. Finally, we will try our simple `X+2` expression again, and this time, it will return `3` successfully.

​

See more: https://eval-expression.net/options

*/

​

using System;

using Z.Expressions;

​

public class Program

{

    public static void Main()

    {

        // Global Context: EvalManager.DefaultContext.VariableFactory = arg => { }

        var context = new EvalContext();

        context.UseCache = false;

​

        try

        {

            var fail = context.Execute("X + 2");

        }

        catch(Exception ex)

        {       

            Console.WriteLine("1 - Exception: " + ex.Message);

        }

        context.VariableFactory = arg =>

            {

                var name = arg.Name;

                if (name == "X")

                {

                    arg.Value = 1;

                    arg.IsHandled = true;

                }

            };

        var r2 = context.Execute("X + 2");

        Console.WriteLine("1 - Result: " + r2);

    }

}