Your first C#, read like TypeScript

You already know how to program. This course is not teaching you loops and functions from scratch; it's teaching you the specific dialect the Fusion team writes, by mapping each idea to the TypeScript you'd reach for by instinct. Start with the biggest shift: C# is compiled, and the compiler is strict.

In Node you edit a .ts file and ts-node runs it, and a type error might still let the program limp along. In C#, dotnet build turns every .cs file into IL (intermediate language) packaged as a DLL, and only then does it run. A type error is a build failure: the program never starts. That strictness is the whole personality of the language, and this module is about getting comfortable inside it.

Here's a whole C# program. Read it as TypeScript with heavier punctuation.

using System;

namespace Hello;

public class Greeter
{
    public string Greet(string name)
    {
        return $"Hello, {name}";
    }
}

class Program
{
    static void Main()
    {
        var greeter = new Greeter();
        Console.WriteLine(greeter.Greet("Rai"));
    }
}

Nearly everything maps. using System; is an import. namespace Hello; groups the file (more in a later lesson). class Greeter is a class. $"Hello, {name}" is a template literal, where backticks become $"...". Console.WriteLine is console.log. The Main method is the entry point, like the top of an index.ts that runs on start.

Two differences jump out and they're worth naming now. First, types come before names: string name, not name: string. A method declares its return type first (public string Greet), the way TS would if it wrote the annotation on the left. Second, statements need semicolons and blocks use braces, always; there's no significant whitespace and no optional-semicolon debate.

The Fusion backend is not one Program.cs, it's a solution (.sln) of several projects (.csproj) that stack into layers. But every one of them is made of files exactly like the one above: namespaces, classes, methods. Get fluent reading this shape and the real codebase stops looking foreign.