1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
|
bf(C++) inherited the struct concept from bf(C) and extended it with the class
concept. Structs are still used in bf(C++), mainly to store and pass around
aggregates of different data types. A commonly used term for these structs is
emi(aggregate) (in some languages known as emi(plain old data)
(i(pod))). Aggregates are commonly used in bf(C++) programs to merely combine
data in dedicated (struct) types. E.g., when a function must return a
tt(double), a tt(bool) and tt(std::string) these three different data types
may be aggregated using a tt(struct) that merely exists to pass along
values. Data protection and functionality is hardly ever an issue. For such
cases bf(C) and bf(C++) use tt(structs). But as a bf(C++) tt(struct) is just a
tt(class) with special access rights some members (constructors, destructor,
overloaded assignment operator) may implicitly be defined. The aggregates
capitalizes on this concept by requiring that its definition remains as simple
as possible. Aggregates show the following characteristics:
itemization(
it() there are no user provided constructors or user provided inherited
constructors (cf. chapter ref(INHERITANCE));
it() its non-static data members have public access rights;
it() no virtual members;
it() when using inheritance, the base classes aren't virtual and only
public inheritance is used.
)
Aggregates can also be arrays, in which case the array elements are the
aggregate's elements. If an aggregate is a tt(struct) its direct base classes
are its elements (if any), followed by the tt(struct's) data members, in their
declaration order. Here is an example:
verb( struct Outer
{
struct Inner
{
int d_int;
double d_double;
};
std::string d_string;
Inner d_inner;
};
Outer out{ "hello", { 1, 12.5} };)
tt(Outer out's d_string) is initialized with tt(hello"), its tt(d_inner)
member has two data members: tt(d_int) is initialized to 1, tt(d_double) to
12.5.
(Designated) initializer lists can also be used (cf. section
ref(INILIST)). Also, often em(structured binding declarations) (cf. section
ref(STRUCTBIND)) can be used to avoid explicitly defining an aggregate data
type.
|
