Should I use PIMPL?

You shouldn’t use PIMPL when virtual calls or any sort of indirection cost your users too much in operation time of their programs: Sequences of repeated small functions calls (and you can’t remove it from API level). Creating and deleting huge amount of small objects (and you can’t remove it from API level).

What does PIMPL?

The pimpl idiom is a modern C++ technique to hide implementation, to minimize coupling, and to separate interfaces. Pimpl is short for “pointer to implementation.” You may already be familiar with the concept but know it by other names like Cheshire Cat or Compiler Firewall idiom.

What is an idiom in C++?

An idiomatic way of writing some code is when you write it in a very specific way because of language-specific idioms that other languages don’t have. For example, in C++, exploiting the RAII idiom leads to ways of writing C++ code managing resources that are idiomatic.

How do you implement Pimpl?

How to implement:

1. Create a separate class ( or struct ) for implementation.
2. Put all private members from the header to that class.
3. Define an Implementation class ( Impl ) in the header file.
4. In the header file create a forward declaration (a pointer), pointing at the implementation class.

How do you use PImpl in C++?

PImpl Idiom in C++ with Examples

1. Create a separate class ( or struct ) for implementation.
2. Put all private members from the header to that class.
3. Define an Implementation class ( Impl ) in the header file.
4. In the header file create a forward declaration (a pointer), pointing at the implementation class.

What is an opaque pointer in C?

In computer programming, an opaque pointer is a special case of an opaque data type, a data type declared to be a pointer to a record or data structure of some unspecified type. Opaque pointers are present in several programming languages including Ada, C, C++, D and Modula-2.

What is an idiom and how does it differ from a pattern?

Idioms are language-specific. Patterns are language-independent design principles, usually written in a “pattern language” (a uniform template) describing things such as the motivating circumstances, pros & cons, related patterns, etc.

What is the idiomatic way?

So the idiomatic way is the way that matches the style of the other code, non-idiomatic way means you are writing the kind of function but in a different way.

Why would you use Unique_ptr instead of a raw pointer when writing a pImpl class?

We define a unique pointer instead of a raw one because the object of the interface type is responsible for the lifetime of the object. Since std::unique_ptr is a complete type it requires a user-declared destructor and copy/assignment operators in order for the implementation class to be complete.

What is an opaque pointer type?

In computer programming, an opaque pointer is a special case of an opaque data type, a data type declared to be a pointer to a record or data structure of some unspecified type. This benefits the programmer as well since a simple interface can be created, and most details can be hidden in another file.

What is are idiom s when we discuss terms related to design patterns?

Idioms represent low-level patterns. In contrast to design patterns, which address general structural principles, idioms describe how to solve implementation-specific problems in a programming language, such as memory management in C++.

What is the Pimpl idiom?

The pImpl Idiom moves the private implementation details of a class into a separate structure. That includes private data as well as non-virtual private methods. The key to this idiom is to only forward-declare the implementation struct in the class header and own onw instance via a pointer.

Is it possible to delete an object in a Pimpl idiom class?

If you have an C++ 11 compiler (or use boost or Qt) you can use a unique/shared pointer around you pimpl idiom class => so you don’t need to delete your object yourself which makes that code much cleaner and safer. MyClass.h in C++ 11 style 1 2

Why use Pimpl in DLLs?

In the Microsoft Windows DLL world, there is another reason to use pImpl – to force all class allocations and deallocations to occur in the DLL. Because of the vagaries of the various C runtime libraries, it is dangerous to provide a DLL that returns allocated memory that the caller is expected to free.

How transparent is the Pimpl approach?

The pimpl approach is transparent from the user viewpoint. Changes made to the IMPLementation structure, internally, affect only the file containing it (User.cpp).