# t00018 - Pimpl pattern
## Config
```yaml
compilation_database_dir: ..
output_directory: puml
diagrams:
  t00018_class:
    type: class
    glob:
      - ../../tests/t00018/**.cc
    using_namespace:
      - clanguml::t00018
    include:
      namespaces:
        - clanguml::t00018

```
## Source code
File t00018_impl.h
```cpp
#pragma once

#include "t00018.h"

namespace clanguml {
namespace t00018 {
namespace impl {

class widget {
    int n;

public:
    void draw(const clanguml::t00018::widget &w) const;
    void draw(const clanguml::t00018::widget &w);
    widget(int n);
};
}
}
}

```
File t00018.h
```cpp
#pragma once

#include <experimental/propagate_const>
#include <iostream>
#include <memory>

namespace clanguml {
namespace t00018 {

namespace impl {
class widget;
}

// Pimpl example based on https://en.cppreference.com/w/cpp/language/pimpl
class widget {
    std::unique_ptr<impl::widget> pImpl;

public:
    void draw() const;
    void draw();
    bool shown() const { return true; }
    widget(int);
    ~widget();

    widget(widget &&);

    widget(const widget &) = delete;
    widget &operator=(widget &&);
    widget &operator=(const widget &) = delete;
};
}
}

```
File t00018.cc
```cpp
#include "t00018.h"
#include "t00018_impl.h"

namespace clanguml {
namespace t00018 {

void widget::draw() const { pImpl->draw(*this); }

void widget::draw() { pImpl->draw(*this); }

widget::widget(int n)
    : pImpl{std::make_unique<impl::widget>(n)}
{
}

widget::widget(widget &&) = default;

widget::~widget() = default;

widget &widget::operator=(widget &&) = default;
}
}

```
File t00018_impl.cc
```cpp
#include "t00018_impl.h"
#include "t00018.h"

namespace clanguml {
namespace t00018 {
namespace impl {

widget::widget(int n)
    : n(n)
{
}

void widget::draw(const clanguml::t00018::widget &w) const
{
    if (w.shown())
        std::cout << "drawing a const widget " << n << '\n';
}

void widget::draw(const clanguml::t00018::widget &w)
{
    if (w.shown())
        std::cout << "drawing a non-const widget " << n << '\n';
}
}
}
}

```
## Generated UML diagrams
![t00018_class](./t00018_class.svg "Pimpl pattern")