All 10 Indexers & Operator Overloading questions
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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 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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How would you implement a fluent, chainable custom '+' operator overload for building an immutable Vector3 math library, and what performance consideration applies for structs?

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Answer

Since Vector3 is typically implemented as a struct for value-semantics and performance, EVERY operator overload should return a NEW Vector3 instance (preserving immutability) rather than mutating either input — and because structs are copied by value, operator overloads on small structs are generally cheap, avoiding heap allocation entirely, unlike an equivalent class-based implementation.
public readonly struct Vector3 {
  public readonly double X, Y, Z;
  public Vector3(double x, double y, double z) { X = x; Y = y; Z = z; }
  public static Vector3 operator +(Vector3 a, Vector3 b) => new(a.X + b.X, a.Y + b.Y, a.Z + b.Z);
  public static Vector3 operator *(Vector3 v, double scalar) => new(v.X * scalar, v.Y * scalar, v.Z * scalar);
}
Vector3 result = (v1 + v2) * 2.0; // fully chainable, zero heap allocation
Real-world example Building a high-performance, allocation-free 3D vector math library for a game engine or physics simulation.

Common follow-ups: Why is 'readonly struct' specifically recommended here, beyond just 'struct'?

Structs Boxing & Unboxing
All 10 Indexers & Operator Overloading questions