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What are top-level statements in C# 9.0?

Ayesha Naeem

Introduced in C# 9.0, top-level statements remove unnecessary ceremonial code from the program.

To write a simple hello world program, a C# program is written like this:

using System;

namespace HelloWorld
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Hello World!");
        }
    }
}

The program needs to include multiple lines of code in order to print a single statement.

With top-level statements, the code can be reduced to simply:

using System;

Console.WriteLine("Hello World!");

Output

Hello World!

Key points about top-level statements

  • It is only possible to include top-level statements in a single file of the application. The compiler will throw an error if it finds top-level statements in multiple source codes.
  • It is not possible to use entry-level statements with a Main() method or program entry point methods.
  • Top-level statements ease the learning process for beginners. They enable a script-like experience, much like what Jupyter provides for programmers adept in C#.
  • A program with top-level statements can contain namespace and type definitions after the top-level statements.
  • Top-level statements can also access command-line arguments.
  • Top-level statements can call asynchronous methods.
  • An integer value returned from a top-level statement can be used as the integer return code of the program.

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