// C# Eval Expression

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

​

// @nuget: Z.Expressions.Eval

​

/*

## Compile Async

​

The C# Eval library doesn't have `CompileAsync` methods. Under the hood, we compile the expression which the [Expression<TDelegate>.Compile method](https://learn.microsoft.com/en-us/dotnet/api/system.linq.expressions.expression-1.compile), which doesn't have a `CompileAsync` method either.

​

However, the `Compile` method support `Async` expression, but the task needs to be handled on the [Execute](/eval-execute#execute-async) part and not the compile part:

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1. **Return a task from the delegate:** `Eval.Compile<Func<Task>>(code)`

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2. **Handle the task** using `await` in the code

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1 - If you **return a task from the delegate** (`Eval.Compile<Func<Task>>(code)`), you need to handle the task with `await` outside the code you want to compile and execute dynamically:

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2 - If you **handle the task**, you need to use `await` inside the code you want to compile and execute dynamically:

​

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

*/

​

using System;

using System.IO;

using System.Threading.Tasks;

using Z.Expressions;

​

public class Program

{

    public static async Task Main()

    {

        var fileName = "myfile.txt";

        await File.WriteAllTextAsync(fileName, "C# Eval Expression from ZZZ Projects");

        // 1. **Return a task from the delegate:** `Eval.Compile<Func<Task>>(code)`

        {

            var compiled1 = Eval.Compile<Func<string, Task<string>>>("File.ReadAllTextAsync(fileName)", "fileName");        

            var text1 = await compiled1(fileName);

            Console.WriteLine(text1);

        }

​

        // 2. **Handle the task** using `await` in the code

        {

            var compiled2 = Eval.Compile<Func<string, string>>("await File.ReadAllTextAsync(fileName)", "fileName");

            var text2 = compiled2(fileName);

            Console.WriteLine(text2);

        }

    }

}