Cpp Notes

C

C: Classes and class hierarchies

C.2: Use class if the class has an invariant; use struct if the data members can vary independently

C.3: Represent the distinction between an interface and an implementation using a class

  • Ideally, and typically, an interface is far more stable than its implementation(s).
  • An explicit distinction between interface and implementation improves readability and simplifies maintenance.
  • C.3 is one of the way to explicitly distinguish between an interface and its implementation "details, other ways include:
    • use a set of declarations of freestanding functions in a namespace
    • an abstract base class
    • a function template with concepts to represent an interface.
    • ...

C.4: Make a function a member only if it needs direct access to the representation of a class

  • Less coupling than with member functions, fewer functions that can cause trouble by modifying object state, reduces the number of functions that needs to be modified after a change in representation.
class Date {
    // ... relatively small interface ...
};

// helper functions have no need for direct access to the representation of a Date
Date next_weekday(Date);
bool operator==(Date, Date);
  • Exception: The language requires operators =, (), [], and -> to be members.

C.5: Place helper functions in the same namespace as the class they support

  • A helper function is a function (usually supplied by the writer of a class) that does not need direct access to the representation of the class, yet is seen as part of the useful interface to the class.
  • Placing them in the same namespace as the class makes their relationship to the class obvious and allows them to be found by argument dependent lookup.
  • This is especially important for overloaded operators.

C.7: Don't define a class or enum and declare a variable of its type in the same statement 

// Bad
struct Data { /* class definitions */ } data{ /* ctor param */ };

// Prefer
struct Data { /* class definitions */ };
Data data{ /* ctor param */ };
  • Mixing a type definition and the definition of another entity in the same declaration is confusing and unnecessary.

C.8: Use class rather than struct if any member is non-public

  • Readability. To make it clear that something is being hidden/abstracted. This is a useful convention.
  • The private data is hidden far from the public data. The data is split in different parts of the class declaration. Different parts of the data have different access.
  • Making struct with private interface decreases readability and complicates maintenance.

C.9: Minimize exposure of members

  • Encapsulation. Information hiding. Minimize the chance of unintended access. This simplifies maintenance.
  • If we want to enforce a relation among members, we need to make them private and enforce that relation (invariant) through constructors and member functions.
  • If the set of direct users of a set of variables cannot be easily determined, the type or usage of that set cannot be (easily) changed/improved.

Subsections

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