// C# Eval Expression

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

​

// @nuget: Z.Expressions.Eval

​

/*

# My First Compilation

​

In this tutorial, we will assume that you have read and understood the concept we introduced in the My First Evaluation tutorial. If you have not read it, make sure you start with this previous tutorial, as we might skip the explanation of a few concepts.

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So what is the major difference between executing and compiling a dynamic code?

​

- The `Compile` method will compile the expression into a method

- The `Execute` method call the `Compile` method under the hood and then execute the returned compiled method.

​

When executing the same expression with the `Execute` method multiple times, it is fast as we retrieve the compiled method from the cache. However, it still takes some time, as we need to create a cache key that has a performance cost. So when you need to execute multiple times the same expression, you should store the compiled method in a local or static variable.

​

How much faster? Using directly the compiled method returned from the `Compile` can be 1000x more quickly than using the `Execute` method. It surely doesn't make any difference if you are only looping on 10 items, as both ways, it will take nearly 0ms. However, if you need to evaluate millions of items, it makes a massive difference between a few milliseconds and seconds.

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

*/

​

using System;

using System.Collections.Generic;

using System.Diagnostics;

using Z.Expressions;

​

public class Program

{

    public static void Main()

    {

        var compiled = Eval.Compile<Func<int>>("1 + 2");

        var clock1 = new Stopwatch();

        var clock2 = new Stopwatch();

        // Eval.Execute

        {

            clock1.Start();

            for(int i = 0; i < 1000000; i++)

            {

                // will always takes compiled method from cache

                var r = Eval.Execute<int>("1 + 2");

            }

            clock1.Stop();

        }

        // Eval.Compile

        {

            clock2.Start();

            for(int i = 0; i < 1000000; i++)

            {

                // will always takes compiled method from cache

                var r = compiled();

            }

            clock2.Stop();

        }

        Console.WriteLine("Time for Eval.Execute: "+clock1.ElapsedMilliseconds+"ms");

        Console.WriteLine("Time for Eval.Compile: "+clock2.ElapsedMilliseconds+"ms");

    }

}