Brownian Bridge™

1. Given `Matrix* p = new SquareMatrix(3, data);`, which method body is invoked by `p->name()` when `name()` is declared `virtual` in `Matrix` and overridden in `SquareMatrix`?

`Matrix::name()` — the static type of `p` is `Matrix*`, so the base version is always called`SquareMatrix::name()` — the vtable attached to the object's dynamic type is consulted at runtimeA compile error: `p->name()` is ambiguous when two definitions exist`Matrix::name()` if compiled with optimisations, `SquareMatrix::name()` otherwise

2. What is the vtable (virtual dispatch table) and when is it set up?

A per-object heap allocation created each time a virtual function is called, torn down on returnA per-class static array of function pointers built by the compiler at compile time; each object stores a hidden `vptr` pointing to itA runtime hash map from method names to function addresses, populated by the dynamic linker at program startA compiler optimisation table that inlines virtual calls after profiling at runtime (PGO)

3. A `SquareMatrix` derived class declares `std::string Name() const;` (capital N) intending to override `virtual std::string name() const;` in `Matrix`. Without `override`, the compiler:

Issues a warning but compiles: the method is treated as a new, unrelated member functionIssues a hard compile error: the name mismatch is detected automaticallySilently compiles and links: `Name()` becomes a new method, `name()` is not overridden; virtual dispatch still calls `Matrix::name()`Links but throws `std::bad_function_call` at runtime when `name()` is called through a base pointer

4. The following code is well-defined: `Matrix* p = new SquareMatrix(3, data); delete p;` — provided `Matrix` declares `virtual ~Matrix() = default;`.

truefalse

5. What is object slicing and what is the correct way to avoid it in a polymorphic quant model hierarchy?

Slicing is when a pointer to a base class is incremented past the end of an array of derived objects; avoid it by using `std::vector<Derived>` instead of raw arraysSlicing is when a derived object is assigned to or copy-constructed into a base object (by value): only the base sub-object is copied, derived members are lost and the `vptr` is reset to the base vtable; avoid it by always handling polymorphic objects via pointer or referenceSlicing is when a `virtual` method is called before the derived constructor finishes; avoid it by not calling virtual methods in constructorsSlicing is a compile-time error triggered by assigning a `SquareMatrix` to a `Matrix` variable; it is prevented by the `explicit` keyword

6. If `Matrix::Matrix()` calls a virtual method `computeRank()`, and `SquareMatrix` overrides `computeRank()`, then during construction of a `SquareMatrix` object the call will invoke `SquareMatrix::computeRank()`.

truefalse

Quiz: Inheritance and Virtual Dispatch

Quick Quiz