C#-Anleitung · 3/6

Types and Data

Dieses Kapitel ist vorerst nur auf Englisch verfügbar.

Every C# type is either a value type or a reference type, and that decides what happens when you assign, pass, or compare values. This chapter covers that split, classes, structs, records, properties, common collections, and null safety.

Value Types vs Reference Types

Built-in types such as int, double, bool, decimal, and DateTime, along with any struct or enum, are value types: the variable holds the data itself, so assignment copies it. Classes, string, arrays, and record classes are reference types: the variable holds a reference to an object, so assignment makes two variables point at the same object.

var p1 = new PointStruct { X = 1 };
var p2 = p1;             // copies the value
p2.X = 99;
Console.WriteLine(p1.X); // 1

var c1 = new PointClass { X = 1 };
var c2 = c1;             // copies the reference
c2.X = 99;
Console.WriteLine(c1.X); // 99

struct PointStruct { public int X; }
class PointClass { public int X; }

string is a reference type, but it is immutable and == compares contents, so it behaves like a value. Use structs for small, immutable data such as coordinates; classes are the default otherwise.

Classes and Properties

A class bundles data (fields and properties) with behavior (methods). Public data is exposed through properties rather than raw fields. A property has get and set accessors, so you can add validation later without breaking any calling code.

var account = new Account("Dana") { Number = "110-123-456" };
account.Deposit(500m);
Console.WriteLine($"{account.Owner}: {account.Balance:F2}");

public class Account
{
    private decimal _balance;

    public Account(string owner) => Owner = owner;

    public string Owner { get; }                 // read-only property
    public string? Memo { get; set; }            // auto-implemented property
    public required string Number { get; init; } // must be set at creation, then frozen

    public decimal Balance => _balance;          // computed property

    public void Deposit(decimal amount)
    {
        if (amount <= 0)
            throw new ArgumentOutOfRangeException(nameof(amount), "Deposit must be positive.");
        _balance += amount;
    }
}

An init accessor allows assignment only during object initialization (the { Number = ... } part), and required turns a forgotten assignment into a compile error. Notice that the statements come first and the class declaration follows: in a file with top-level statements, type declarations must come after the statements.

Records

Records are a concise way to declare types whose main job is carrying data. A positional record gets a constructor, read-only properties, value-based equality, and a readable for free.

Fragen zu diesem Kapitel?

Types and Data

Value Types vs Reference Types

Classes and Properties

Records

Collections

Nullable Reference Types

Summary

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