C# Eval - Compile Method - Compile Async

CSharp · Console

/Program.cs

// 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:

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

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

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:

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);
		}
	}
}