# The PImpl Idiom and the std:indirect Type in C++26

Discover how the PImpl idiom works in C++ programming and the conveniences brought by C++26.

- **Source:** [Hacker News](https://news.ycombinator.com)
- **Published:** 2026-07-24
- **Topic:** [Software & Engineering](https://brifing.si/c/engineering)
- **Original article:** <https://mariusbancila.ro/blog/2026/07/23/the-pimpl-idiom-and-the-cpp26-stdindirect-type/>
- **On Brifing:** https://brifing.si/s/4e7c9bc7-9492-44f3-b6bb-f8c3887ba6d5

## What is the PImpl Idiom?

The PImpl (Pointer to Implementation) idiom is a programming technique used to hide the implementation details of a class. This technique separates the interface from the implementation, minimizing compile-time dependencies.

## Implementation with Raw Pointers

The PImpl idiom can be implemented using raw pointers. In this approach, the 'Rule of Five' is followed, and all five special member functions of the class are defined. These functions are essential for resource management.

## Widget Example

The Widget class represents a UI element and has a clickable structure. Each click increments a counter, and these details are hidden behind an implementation class. The Widget class accesses these details through a pointer.

## Constness Issue

Constness does not propagate from Widget to Impl in the Widget class. This means that even within a const method, the state of the Impl object can be changed. This situation can lead to unexpected results.

## Move Semantics Issue

When move semantics are used, the pimpl_ pointer of the moved Widget object becomes null. In this case, any function called using the pointer results in undefined behavior (UB).

## Solution with std::unique_ptr

The PImpl idiom can be implemented more simply using std::unique_ptr from C++11. This automates resource management and provides a safer solution compared to using raw pointers.

## The New Widget Class

When std::unique_ptr is used, the copy constructor and copy assignment operator of the Widget class are explicitly defined. Other special member functions are defaulted by the compiler.

## Conveniences with C++26

The std::indirect type introduced with C++26 will further simplify the implementation of the PImpl idiom. This new type will make pointer management more efficient and the code more readable.

## Sources covering this story

- https://mariusbancila.ro/blog/2026/07/23/the-pimpl-idiom-and-the-cpp26-stdindirect-type/ — 

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_Summary written by Brifing from the original reporting. Copyright in the original article belongs to its publisher; read the full piece at the link above._