Error cs8803 top level statements must precede namespace and type declarations

Earlier I was putting some code together for an example. I got the following error (Top-level statements must precede namespace and type declarations):

Error	CS8803	Top-level statements must precede namespace and type declarations.	ConsoleApp2	C:UserspetersourcereposConsoleApp2ConsoleApp2Program.cs	25

The code looked like the following:

public static class StringExtensions
{
    public static string ToCommaSeperatedString(this IEnumerable<string> list)
    {
        return string.Join(",", list);
    }
}

var someList = new List<string>
{
   "A","B","C"
};

Console.WriteLine(someList.ToCommaSeperatedString());

In the above we declare a new type of class (StringExtensions) and then we create a list of strings, however with Top-level statements (TLS) you must declare your namespaces and types — for example classes — first. There are two solution to this, the code can be rearranged so that the class is defined last:

var someList = new List<string>
{
   "A","B","C"
};

Console.WriteLine(someList.ToCommaSeperatedString());

public static class StringExtentions
{
    public static string ToCommaSeperatedString(this IEnumerable<string> list)
    {
        return string.Join(",", list);
    }
}

Alternatively we can go back to the old way of making entry points with a static void Main method:

class Program
{
    static void Main(string[] args)
    {
        var someList = new List<string>
        {
            "A","B","C"
        };

        Console.WriteLine(someList.ToCommaSeperatedString());
    }
}

public static class StringExtentions
{
    public static string ToCommaSeperatedString(this IEnumerable<string> list)
    {
        return string.Join(",", list);
    }
}

I hope you found this helpful, please leave a comment down below if you did!

Источник

C# 9.0 introduced top-level statements that allow you to skip all the boilerplate code and get to the point quickly. No need to declare a namespace, class, or even a Main() method. Just open your editor and start writing beautiful C# code.

Writing a simple console program in C# has always involved a ton of ceremony. You have to create a class named Program. Then declare the Main method that is public, static, void, and takes an array of strings as arguments. Here is an example.

using System;

class Program
{
    static void Main(string[] args)
    {
        int sum = 45 + 50;
        Console.WriteLine(sum);
    }
}

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In the above example, there is too much clutter. There are only two lines that are actually doing something. When a beginner reads the above program, it can feel quite overwhelming.

What is System? Why are we using it?
What is a class? Where are the students?
What is static, why is it void?
What is args?

The essential part in the above program is the code that adds and displays the sum of two numbers. Rest is just ceremony.

In C# 9.0, you can simply write this:

int sum = 45 + 50;
System.Console.WriteLine(sum);

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Using sharplab, we can see how the C# compiler transforms this code before it’s compiled. Notice that the Program class and Main method are still getting generated behind the scenes, but you don’t have to write them.

using System;
using System.Diagnostics;
using System.Reflection;
using System.Runtime.CompilerServices;
using System.Security;
using System.Security.Permissions;

[CompilerGenerated]
internal static class <Program>$
{
    private static void <Main>$(string[] args)
    {
        int value = 95;
        Console.WriteLine(value);
    }
}

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What happens to the command-line arguments?

They are still accessible using the args array. You can run the following code using dotnet run hello, and it will print hello to the console.

System.Console.WriteLine(args[0]);

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How can I return a status code?

Just return it, as you normally would. For example,

System.Console.WriteLine("Hello");
return 0;

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Can I have multiple files with top-level statements?

No. Only one file in your application can use top-level statements. The compiler throws an error when it finds multiple files containing top-level statements.

Can I create classes in the same file?

Yes, the only requirement is that the top-level statements should come before any type declaration. For example,

using System;

var animal = new Animal { Name = "Dog" };
Console.WriteLine(animal.Name);

class Animal
{
    public string Name { get; set; }
}

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You can’t create a class and then write your statements. For example, this code is invalid.

using System;

class Animal
{
    public string Name { get; set; }
}

var animal = new Animal { Name = "Dog" };
Console.WriteLine(animal.Name);

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It throws the following error.

error CS8803: Top-level statements must precede namespace and type declarations.

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Top-level statements make C# beginner-friendly, giving it a scripty feel, like Ruby or Python. They also make simple programs clear and expressive. If you just want to understand a concept in C# or try out a base class library, you can quickly do so using the top-level statements. They are also great for small tools and utilities.

Did I miss anything? Let me know.

Timeless DEV post…

How to write a kickass README

Arguably the single most important piece of documentation for any open source project is the README. A good README not only informs people what the project does and who it is for but also how they use and contribute to it.

If you write a README without sufficient explanation of what your project does or how people can use it then it pretty much defeats the purpose of being open source as other developers are less likely to engage with or contribute towards it.

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class PlayerControls : MonoBehaviour {
    public KeyCode moveUp = KeyCode.W;
    public KeyCode moveDown = KeyCode.S;
    public float speed = 10.0f;
    public float boundY = 2.25f;
    private RigidBody2D rb2d;
    }
{
    // Start is called before the first frame update
    void Start() {
        rb2d = GetComponent<RigidBody2D>();
    }

    // Update is called once per frame
    void Update() {
        var vel = rb2d.velocity;
        if (Input.GetKey(moveUp)) {
            vel.y = speed;
        }
        else if (Input.GetKey(moveDown)) {
            vel.y = -speed;
        }
        else {
            vel.y = 0;
        }
        rb2d.velocity = vel;

        var pos = transform.position;
        if (pos.y > boundY) {
            pos.y = boundY;
        }
        else if (pos.y < -boundY) {
            pos.y = -boundY;
        }
        transform.position = pos;
    }
}

I belive it is something to do with this:

public class PlayerControls : MonoBehaviour {
    public KeyCode moveUp = KeyCode.W;
    public KeyCode moveDown = KeyCode.S;
    public float speed = 10.0f;
    public float boundY = 2.25f;
    private RigidBody2D rb2d;
    }

But I am not sure how to fix it since the site doesnt specify where I need to put it.

Источник

How to write a kickass README

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