Introduction to Classes Flashcards
What is the focus in procedural programming?
To create functions that implement our program logic. We pass data objects to these functions, those functions perform operations on the data and potentially return a result
What is the focus in object-oriented programming?
To create program defined data types that contain properties and well defined behaviours
class invariant
a condition that must be true for the lifetime of an object for the object to remain in a valid state
invalid state
an object that has a violated class invariant. Unexpected or undefined behaviour may result from further use of that object
class
program defined compound type with data, and functions which work on that data
member functions
functions that belong to a class type
implicit object
the object that a member function is called on
non member functions
name for functions that are not member functions
what should you do if your class has no data members
use a namespace instead
const member functions
member function that guarantees it will not modify the object or call any non-const member functions (as they may modify the object)
a member function that does not (and will not ever) modify the state of the object should be made const, so that it can be called on both non-const and const objects
access level
each member of a class has an access level that determines who can access that member.
access levels are defined on a per class basis not a per object basis
access controls
access level system informally called this
public members
members of a class type that do not have any restrictions on how they can be accessed. Public members can be accessed by anyone (as long as they are in scope). This includes other members of the same class or code outside of the class
the public
code that exists outside the members of a given class type
includes:
non-member functions
members of other class types
What is the default access level for all members of a struct?
public
private members
members of a class type that can only be accessed by other members of the same class
What is the default access level for all members of a class?
private
is a class with private members an aggregate?
no and therefore it cannot use aggregate initialisation
how should you name private members?
starting with a m_ prefix. his helps distinguih them from the names of local variables, function parameters and member functions
access specifier
allows you to explicitly set the access level of our members
should structs use access specifiers?
they should avoid them, therefore all their members default to public
access function
a trivial public member function whose job is to retrieve or change the value of a private member variable. Access function come in two flavours: getters and setters
Getters
sometimes called accessors, are public member functions that return the value of a private member variable
setters
sometimes called mutators, are public member fucntions that set the value of a private member variable.
interface
this determines how a user of the class type will interact with objects of the class type. Because only public members can be accessed from outside of the class type, the public members of a class type form its interface.
public interface
an interface composed of only public members
implementation of a class type
the code that actually makes the class behave as intended. This includes both the member variables that store data, and the bodies of the member functions that contain the program logic and manipulate the member variables
data hiding / information hiding / data abstraction
technique used to enforcethe separation of the interface and implementation by hiding the implementation of a program defined data type from users
encapsulation
sometimes used to refer to data hiding or to refer to the bundling of data and functions together (without regard for access controls) so its use can be ambiguous
What order should you define the members in your class and why?
Prefer to declare your public members first and your private members last. This spotlights the public interface and de-emphasises implementation details
constructor
a special member function that is used to initialise class type objects. A matching constructor must be found in order to create a non-aggregate class type object
member initialiser list
allows you to initialise your member variables from within a constructor. Member variables in a member initialiser should be listed in the order that they are defined in the class. Prefer using the member initialiser list to initialise your members over assigning values in the body of the constructor
default constructor
a constructor that takes no parameters (or has all default parameters). The default constructor is used if no initialisation values are provided.
implicit default constructor
If a non-aggregate class type object has no user-declared constructors, the compiler will generate a default constructor (so that the class can be value or default initialised)
constructor chaining
when a constructor delegates construction to another constructor
delegating constructors
a constructor that delegates using constructor chaining
can constructors delegate and initialise
no only one or the other
temporary / unamed / anonymous object
an object that has no name and exists only for the duration of a single expression
copy constructor
a constructor you use to initialise an object with an existing object of the same type
implicit copy constructor
if you do not provide a copy constructor for your class c++ will create a public one for you that does memberwise initialisation
as-if rule
the compiler can modify a program however it likes in order to produce more optimised code, so long as those modifications do not affect a program’s observable behaviour
One exception to the rule is copy elision
copy elision
a compiler optimization technique that allows the compiler to remove unnecessary copying of objects
elided
we say the constructor has been elided when the compiler optimised away a call to the copy constructor
user defined conversion
a function written to convert a value to or from a program defined type
converting constructor
constructor that can be used to perform an implicit conversion
are all constructors converting constructors?
they are in their default state
explicit
we use this keyword to tell the compiler a constructor should not be used as a converting constructor
what can explicit constructors not be used for?
copy initialisation
copy list initialisation
implcit conversions
what constructors should you mark as explicit
any constructor that takes a single argument
what constructors should you leave as implicit?
copy or move constructors (as these do not perform conversions)
cases where the conversion between types is both semantically equivalent and performant
are constexpr member functions const?
not implicitly
