# t00019 - Layercake pattern
## Config
```yaml
compilation_database_dir: ..
output_directory: puml
diagrams:
  t00019_class:
    type: class
    glob:
      - ../../tests/t00019/**.cc
    using_namespace:
      - clanguml::t00019
    include:
      namespaces:
        - clanguml::t00019

```
## Source code
File t00019_layer2.h
```cpp
#pragma once

namespace clanguml {
namespace t00019 {

template <typename LowerLayer> class Layer2 : public LowerLayer {

    using LowerLayer::LowerLayer;

    using LowerLayer::m1;

    using LowerLayer::m2;

    int all_calls_count() const
    {
        return LowerLayer::m1_calls() + LowerLayer::m2_calls();
    }
};
}
}

```
File t00019_base.h
```cpp
#pragma once

#include <string>

namespace clanguml {
namespace t00019 {

class Base {

    Base() = default;

    virtual ~Base() = default;

    virtual int m1() { return 2; }

    virtual std::string m2() { return "two"; }
};
}
}

```
File t00019_layer1.h
```cpp
#pragma once

#include <iostream>
#include <string>

namespace clanguml {
namespace t00019 {

template <typename LowerLayer> class Layer1 : public LowerLayer {

    using LowerLayer::LowerLayer;

    int m1() override
    {
        std::cout << "m1 called\n";
        return LowerLayer::m1();
    }

    std::string m2() override
    {
        std::cout << "m2 called\n";
        return LowerLayer::m2();
    }
};
}
}

```
File t00019.cc
```cpp
#include "t00019_base.h"
#include "t00019_layer1.h"
#include "t00019_layer2.h"
#include "t00019_layer3.h"

#include <memory>

namespace clanguml {
namespace t00019 {

class A {
public:
    std::unique_ptr<Layer1<Layer2<Layer3<Base>>>> layers;
};
}
}

```
File t00019_layer3.h
```cpp
#pragma once

#include <string>

namespace clanguml {
namespace t00019 {

template <typename LowerLayer> class Layer3 : public LowerLayer {

    using LowerLayer::LowerLayer;

    virtual int m1() override
    {
        m_m1_calls++;
        return LowerLayer::m1();
    }

    virtual std::string m2() override
    {
        m_m2_calls++;
        return LowerLayer::m2();
    }

    int m1_calls() const { return m_m1_calls; }

    int m2_calls() const { return m_m2_calls; }

private:
    int m_m1_calls{};
    int m_m2_calls{};
};
}
}

```
## Generated UML diagrams
![t00019_class](./t00019_class.svg "Layercake pattern")