# t20070 - Test case for sequence diagram with coroutines
## Config
```yaml
diagrams:
  t20070_sequence:
    type: sequence
    glob:
      - t20070.cc
    include:
      namespaces:
        - clanguml::t20070
    using_namespace: clanguml::t20070
    generate_condition_statements: true
    generate_return_types: true
    from:
      - function: "clanguml::t20070::tmain()"
```
## Source code
File `tests/t20070/t20070.cc`
```cpp
#include <coroutine>
#include <cstdint>
#include <exception>
#include <iostream>

namespace clanguml::t20070 {

void foo() { }
//
// Based on https://en.cppreference.com/w/cpp/language/coroutines
//

struct AwaitableFoo {
    bool await_ready() const noexcept { return false; }

    void await_suspend(std::coroutine_handle<> h) const noexcept { h.resume(); }

    void await_resume() const noexcept { }
};

template <typename T> struct Generator {
    struct promise_type;
    using handle_type = std::coroutine_handle<promise_type>;

    struct promise_type // required
    {
        T value_;
        std::exception_ptr exception_;

        Generator get_return_object()
        {
            return Generator(handle_type::from_promise(*this));
        }

        std::suspend_always initial_suspend() { return {}; }

        std::suspend_always final_suspend() noexcept { return {}; }

        void unhandled_exception()
        {
            exception_ = std::current_exception();
        } // saving
          // exception

        template <std::convertible_to<T> From> // C++20 concept
        std::suspend_always yield_value(From &&from)
        {
            value_ = std::forward<From>(from); // caching the result in promise
            return {};
        }

        void return_void() { }
    };

    handle_type h_;

    Generator(handle_type h)
        : h_(h)
    {
    }

    ~Generator() { h_.destroy(); }

    explicit operator bool()
    {
        fill();
        return !h_.done();
    }

    T operator()()
    {
        fill();
        full_ = false;
        return std::move(h_.promise().value_);
    }

private:
    bool full_ = false;

    void fill()
    {
        if (!full_) {
            h_();
            if (h_.promise().exception_)
                std::rethrow_exception(h_.promise().exception_);

            full_ = true;
        }
    }
};

class FibonacciGenerator {
public:
    Generator<unsigned long long> generate_sequence(unsigned n)
    {
        if (n == 0) {
            co_return;
        }

        co_yield 0;

        if (n == 1)
            co_return;

        co_yield 1;

        if (n == 2)
            co_return;

        unsigned long long a = 0;
        unsigned long long b = 1;

        for (unsigned i = 2; i < n; ++i) {
            unsigned long long s = a + b;
            co_yield s;
            a = b;
            b = s;
        }
    }
};

template <typename T>
Generator<T> template_generator(T start, T step, unsigned count)
{
    for (unsigned i = 0; i < count; ++i) {
        co_yield start + i *step;
    }
}

Generator<unsigned long long> fibonacci_sequence(unsigned n)
{
    if (n == 0) {
        foo();
        co_return;
    }

    if (n > 94)
        throw std::runtime_error(
            "Too big Fibonacci sequence. Elements would overflow.");

    co_await AwaitableFoo{};

    co_yield 0;

    if (n == 1)
        co_return;

    co_yield 1;

    if (n == 2)
        co_return;

    unsigned long long a = 0;
    unsigned long long b = 1;

    for (unsigned i = 2; i < n; ++i) {
        unsigned long long s = a + b;
        co_yield s;
        a = b;
        b = s;
    }
}

int tmain()
{
    try {
        auto gen = fibonacci_sequence(10ULL);

        for (int j = 0; gen; ++j)
            std::cout << "fib(" << j << ")=" << gen() << '\n';

        FibonacciGenerator fib_gen;
        auto class_gen = fib_gen.generate_sequence(5ULL);

        for (int j = 0; class_gen; ++j)
            std::cout << "class_fib(" << j << ")=" << class_gen() << '\n';

        auto template_gen = template_generator<unsigned long long>(10, 5, 3);

        for (int j = 0; template_gen; ++j)
            std::cout << "template_gen(" << j << ")=" << template_gen() << '\n';
    }
    catch (const std::exception &ex) {
        std::cerr << "Exception: " << ex.what() << '\n';
    }
    catch (...) {
        std::cerr << "Unknown exception.\n";
    }

    return 0;
}
} // namespace clanguml::t20070

```
## Generated PlantUML diagrams
![t20070_sequence](./t20070_sequence.svg "Test case for sequence diagram with coroutines")
## Generated Mermaid diagrams
![t20070_sequence](./t20070_sequence_mermaid.svg "Test case for sequence diagram with coroutines")
## Generated JSON models
```json
{
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      },
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    {
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      },
      "type": "class"
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    {
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      "full_name": "clanguml::t20070::template_generator<unsigned long long>(unsigned long long,unsigned long long,unsigned int)",
      "id": "9999851530951415081",
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                  ],
                  "name": "for",
                  "type": "loop"
                },
                {
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                  "condition_text": "int j = 0; gen; ++j",
                  "messages": [
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```
## Generated GraphML models