ATL Copy Policy Classes

Copy Policy Classes

Copy Policy Classes are utility classes that are used to initialize, copy, and delete data. It allows for defining copy semantics and conversion of different data types. 

The following templates in ATL use the copy policy classes in their implementation:

• Replace the DestinationType and SourceType with any random data types of the policy class.
• Use init to initialize the data
• Use Copy for copying the data
• Use destroy to delete the data

Requirements

• The First parameter we have to copy will receive a pointer to the initialized data using init.
• The destroy will only receive a  pointer to the data that was initialized using init or copies using Copy.

Standard Implementations

ATL provides two template classes, which are copy policy classes:

• _Copy
• _CopyInterface 

Since the _Copy class only provides a single template parameter to indicate DestinationType and SourceType, it only supports homogeneous copying.

The _CopyInterface class offers a copying interface pointer implementation that complies with COM standards.

Custom Implementations

ATL provides two template classes, which are copy policy classes:

• GenericCopy 
• MapCopy

GenericCopy

In this, you'll define SourceType and DestinationType as the template arguments.

MapCopy

MapCopy allows you to provide the type of map in which the data is stored and the destination type since it assumes that the data being duplicated is saved into a map in the style of the C++ Standard Library.

Frequently Asked Questions

What are copy constructors in C++?

The copy constructor is referred to as a member function since it initializes a new object using another object from the same class.

What are C++ templates?

In C++, a template is a design pattern or recipe for developing a generic class or function.

What is a template in OOP?

A template is a section of code that may be duplicated and altered to suit a particular situation.

What does DLL stand for?

When necessary, larger applications might load a collection of smaller programs known as a dynamic link library (DLL) to carry out specialized functions.

What are the types of templates in C++?

There are three types of templates in C++: function templates, class templates, and variable templates.

Conclusion

This blog has extensively discussed ATL Copy Policy Classes. We hope this blog has helped you enhance your knowledge about the Standard Implementation and custom implementation of Policy Classes.

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