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What is an indexer, and how does it let a custom class support square-bracket syntax like an array? Which operators can be overloaded in C#, and which ones (like && and ||) generally CANNOT be overloaded directly? How do you overload comparison operators like < and >, and what consistency rule must they maintain relative to Equals()? How do you define a custom implicit or explicit conversion operator between your type and another type? How would you implement a multi-dimensional indexer, like a Matrix class supporting matrix[row, col] syntax? How do you overload the true/false operators to make a custom type usable directly in an 'if' statement or as a boolean condition? How would you implement a fluent, chainable custom '+' operator overload for building an immutable Vector3 math library, and what performance consideration applies for structs? How do you implement the 'checked' operator overload variant (introduced in C# 11) to provide overflow-checking behavior for a custom numeric type? How would you use an indexer together with a custom enumerator (implementing IEnumerable) to build a fully iterable, indexable custom collection class?
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C# › Indexers & Operator Overloading

How do you overload the '+' operator to support adding two custom objects together?

Beginner

Answer

Declare a 'public static' method named 'operator +' taking two parameters of your type (or your type and another compatible type), returning the result — the compiler then lets you use the normal '+' syntax directly on instances of your type.
public struct Money {
  public decimal Amount;
  public static Money operator +(Money a, Money b) => new Money { Amount = a.Amount + b.Amount };
}
Money total = new Money { Amount = 10 } + new Money { Amount = 5 };
Console.WriteLine(total.Amount); // 15
Real-world example Allowing two Money, Vector, or Complex number instances to be combined naturally with the '+' operator instead of a named method.

Common follow-ups: Why must operator overloads always be declared as 'public static' members?

Structs Boxing & Unboxing
All 10 Indexers & Operator Overloading questions