Python descriptor details

C++: struct Vs. class

Firstly, in C++, Both class and struct declare a class. The struct is intended for backward compatibility with C(different with C, because it is a class).

Accessibility

• struct: have default public members and bases. It means when inheriting, struct defaults to public inheritance.
• class: have default private members and bases. It means when inheriting, class defaults to private inheritance.

Both directives allows a mixture of public, protected and private data and member functions.
In fact, two formats below are absolutely equivalent in every way except their name:

struct Foo
{
    int x;
};

class Bar
{
    public:
        int x;
};

When to use:

• If we want to use structs as plain-old-data(POD) structures without any class-like features, then we need to use struct. Note, the POD means that is a class (whether defined with the keyword struct or the keyword class) without constructors, destructors and virtual members functions.
• Then other situations is suitable to use class.

Using struct as lambda function

struct Compare {bool operator() {...}};
std::sort(collection.begin(), collection.end(), Compare());

However, the lambda function has been supported in C++11 by all the major compilers.

Constructor

Since both directives are class, both are able to have constructor and destructor.
But some people would like to stick with the struct keyword for classes without member functions, because the resulting definition “looks like” a simple structure from C.

References

• when to use
• POD
• Constructor
• overflow

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