Blog
Mert Özen's blog posts on software development, backend, frontend, and DevOps.
Classes and Objects in C#: Writing Your First Own Type
A class is a recipe, an object is what it produces in memory. The first Book class with fields and methods, this, what being a reference type means, identity comparison with ==, null and NullReferenceException, and how classes are laid out in files and namespaces.
Fields, Properties and Constructors in C#: Building Objects Right
The parameterless constructor that disappears once you write your own, private and readonly fields, a validating property, auto-properties, get-only, private set, init and computed properties, constructor chaining and the order in which initializers run.
Encapsulation and Access Modifiers in C#: public, private, protected, internal
Why a get-only List property protects nothing, keeping invariants inside the object, IReadOnlyList versus AsReadOnly, the six access modifiers and their defaults, private belonging to the type, and the assembly boundary with internal and InternalsVisibleTo.
Static Members, Static Classes and Extension Methods in C#
Static fields and methods that belong to the type, the absence of this in static methods, const versus static readonly and when the static constructor runs, static classes, an ISBN-validating extension method, the rules of extensions and the threading trap of shared static state.
Inheritance in C#: base, sealed and the Constructor Chain
Inheritance with Product, Book and EBook: what a derived class sees and protected, the constructor chain with base and the reverse order of field initializers, upcasting, downcasting, is and as, stopping derivation with sealed, and how an Order derived from List breaks encapsulation.
Polymorphism in C#: virtual, override, new and Abstract Classes
Letting the runtime decide with virtual and override, an if-free cart loop for shipping costs, base calls and overriding ToString, hiding with new and the CS0114 trap, abstract classes and the template method, sealed override and the NullReferenceException of calling a virtual method from a constructor.
Interfaces in C#: Multiple and Explicit Implementation, Default Interface Methods
An interface is a contract: CS0535 and CS0144, a class implementing several interfaces, explicit implementation for same-named members and its examples in the BCL, default interface methods callable only through the interface, choosing between an interface and an abstract class, and testable code by putting the clock behind an interface.
struct vs class in C#: Copy Semantics and readonly struct
A struct is a value type: the copies hidden in properties, indexers and foreach, C# 10 parameterless constructors versus default, the inheritance rules of structs, an immutable Money with readonly struct and with, the second copy created by boxing, struct equality and when to make a type a struct.
C# record and record struct: Value Equality and the with Expression
The members the compiler generates for a record, copying with with, positional and nominal records, EqualityContract in inheritance, C# 10's record struct, and when to pick a record.
Equality and Comparison in C#: Equals, GetHashCode, IEquatable and IComparable
Reference and value equality, the Equals and GetHashCode contract, IEquatable<T> and the == operator, equality in structs, sorting with IComparable<T>, and comparers that decide from the outside.
Operator Overloading and Indexers in C#
Why operators are static methods and the trap that comes with it, arithmetic and comparison operators for Money, the compiler's rules, implicit/explicit conversions, indexers and Index/Range support.
Composition in C# and an Introduction to SOLID
How a cart derived from List leaks its rules, having instead of being with composition, the five SOLID principles through Bookstore examples, and the cost of overdoing them.