enum class and using-aliases

The magic-string problem

Functions that take "admin", "editor", "viewer" as strings are a bug factory: typos compile, casing drifts, and the set of valid values lives only in documentation. The fix is a closed set with a type:

enum class Role { Viewer, Editor, Admin };

Role role = Role::Editor;

switch (role) {
    case Role::Viewer: /* ... */ break;
    case Role::Editor: /* ... */ break;
    case Role::Admin:  /* ... */ break;
}

Why enum class, not plain enum

• Scoped: values are Role::Editor, never bare Editor — no namespace pollution.
• Strongly typed: Role does not silently convert to int; you cannot accidentally compare a Role with a number or pass it where an int is expected. (Plain pre-C++11 enum leaks values into the enclosing scope and converts to int — legacy code compat, not a recommendation.)
• Switch-checked: with -Wall -Wextra, GCC warns when a switch over a Role misses a case (add a default or handle every enumerator).

using: type nicknames

using Inventory = std::map<std::string, int>;
using Scores = std::vector<int>;

Inventory stock;             // reads like the domain
std::vector<std::vector<int>> grid;
using Grid = std::vector<std::vector<int>>;

using (modern; prefer it over C's typedef) gives long types honest names. It is documentation with compiler enforcement: change the alias once, every user follows.

Modeling exercise ahead

The checkpoint asks you to design struct Order { ... } with enum class Status { ... } — one glance at the type definitions should explain the whole business domain.