# t20012 - Lambda expression call sequence diagram test case
## Config
```yaml
compilation_database_dir: ..
output_directory: puml
diagrams:
  t20012_sequence:
    type: sequence
    glob:
      - ../../tests/t20012/t20012.cc
    include:
      namespaces:
        - clanguml::t20012
    using_namespace:
      - clanguml::t20012
    start_from:
      - function: "clanguml::t20012::tmain()"
```
## Source code
File t20012.cc
```cpp
#include <algorithm>
#include <functional>
#include <memory>
#include <optional>
#include <utility>

namespace clanguml {
namespace t20012 {
struct A {
    void a() { aa(); }

    void aa() { aaa(); }

    void aaa() { }
};

struct B {
    void b() { bb(); }

    void bb() { bbb(); }

    void bbb() { }

    void eb() { }
};

struct C {
    void c() { cc(); }

    void cc() { ccc(); }

    void ccc() { }
};

struct D {
    int add5(int arg) const { return arg + 5; }
};

class E {
    std::optional<std::shared_ptr<B>> maybe_b;
    std::shared_ptr<A> a;

public:
    template <typename F> void setup(F &&f) { f(maybe_b); }
};

template <typename F> struct R {
    R(F &&f)
        : f_{std::move(f)}
    {
    }

    void r() { f_(); }

    F f_;
};

void tmain()
{
    A a;
    B b;
    C c;

    // The activity shouldn't be marked at the lambda definition, but
    // wherever it is actually called...
    auto alambda = [&a, &b]() {
        a.a();
        b.b();
    };

    // ...like here
    alambda();

    // There should be no call to B in the sequence diagram as the blambda
    // is never called
    [[maybe_unused]] auto blambda = [&b]() { b.b(); };

    // Nested lambdas should also work
    auto clambda = [alambda, &c]() {
        c.c();
        alambda();
    };
    clambda();

    R r{[&c]() { c.c(); }};

    r.r();

    D d;

    std::vector<int> ints{0, 1, 2, 3, 4};
    std::transform(ints.begin(), ints.end(), ints.begin(),
        [&d](auto i) { return d.add5(i); });

    // TODO: Fix naming function call arguments which are lambdas
    //    E e;
    //
    //    e.setup([](auto &&arg) mutable {
    //        // We cannot know here what 'arg' might be
    //        arg.value()->eb();
    //    });
}
}
}
```
## Generated UML diagrams
![t20012_sequence](./t20012_sequence.svg "Lambda expression call sequence diagram test case")