Aggregate Initialization for Nested Structures

Aggregate initialization simplifies the initialization of objects with nested structures by allowing you to provide values in a nested list. This method is particularly useful for initializing complex types in a concise and readable manner.

Consider the following example with nested structures:

1#include <iostream>
2
3struct Point {
4  int x, y;
5};
6
7struct Line {
8  Point start, end;
9};
10
11int main() {
12  Line myLine{{0, 0}, {10, 10}};  
13  std::cout << "Start: (" << myLine.start.x
14    << ", " << myLine.start.y << ")\n";
15  std::cout << "End: (" << myLine.end.x
16    << ", " << myLine.end.y << ")\n";
17}

1Start: (0, 0)
2End: (10, 10)

In this example, Line is an aggregate that contains two Point objects. Using aggregate initialization, we can initialize myLine with nested braces. Each Point structure is initialized with its own list of values.

Aggregate initialization also works with more complex nesting:

1#include <iostream>
2#include <string>
3
4struct Address {
5  std::string city, country;
6};
7
8struct Person {
9  std::string name;
10  int age;
11  Address address;
12};
13
14int main() {
15  Person p{"Alice", 30, {"New York", "USA"}}; 
16  std::cout << p.name << ", "
17    << p.age << ", "
18    << p.address.city << ", "
19    << p.address.country;
20}

1Alice, 30, New York, USA

Here, the Person structure contains a nested Address structure. Aggregate initialization allows us to initialize the Person object in a single statement, providing a list of values for each nested structure.

Aggregate initialization is convenient for initializing complex types, as it maintains readability and reduces boilerplate code.

However, it is essential to ensure that the structures being initialized are aggregates, meaning they do not have private or protected members, non-public base classes, or user-provided constructors.