boost-di/doc/cppcon-2018/index.html at cpp14 · clayne/boost-di · GitHub

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<title>[Boost].DI - inject all the things!</title>

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 data-separator="^====+$"
 data-separator-vertical="^----+$">
<script type="text/template">

#### CppCon, 2018

# [Boost].DI
# Inject all the things!

Kris Jusiak, Quantlab Financial

#### [kris@jusiak.net](mailto:kris@jusiak.net) | [@krisjusiak](https://twitter.com/krisjusiak) | [linkedin.com/in/kris-jusiak](https://www.linkedin.com/in/kris-jusiak)

----

### Dependency Injection

> "Don't call us, we'll call you", Hollywood principle

```cpp
 No DI | DI
-------------------------------+-------------------------------------------
class cppcon_talk { | class cppcon_talk {
 private: /*Tightly coupled*/ | public: /*Dependency Injection!*/
 room room_{'Eniac'}; | cppcon_talk(room, speaker, attendees);
 speaker speaker{"Kris"}; |
 attendees attendees_{}; | private:
}; | room room_{};
 | speaker speaker_{};
 | attendees attendees_{};
 | };
```
<!-- .element: style="margin-left:0%; width:105%" -->

----

### C++ Dependency Injection Library - [[Boost].DI](https://github.com/boost-ext/di)

* One header - 3k LOC - ([boost/di.hpp](https://raw.githubusercontent.com/boost-ext/di/cpp14/include/boost/di.hpp)) / generated
* Neither Boost nor STL is required
* No 'if's, 'virtual's, 'exception's, macros, run-time errors

**Disclaimer** `[Boost].DI` is not an official Boost library

----

### Inject by default (create object graph)

```cpp
class room {}; class speaker {}; class attendees {};

class cppcon_talk {
 public:
 cppcon_talk(const room&, const speaker&, attendees&);
};
```
<!-- .element: style="margin-left:0%; width:105%" -->

```cpp
 Manual DI | [Boost].DI
-------------------------------------+-------------------------------------
 auto room = room{}; |
 auto speaker = speaker{}; |
 auto attendees = attendees{}; | auto talk =
 | di::create<cppcon_talk>();
 auto talk = cppcon_talk{room, |
 speaker, |
 attendees}; |
```
<!-- .element: style="margin-left:0%; width:105%" -->

----

### Inject / refactor

```cpp
class room {}; class speaker {}; class attendees {};

class cppcon_talk {
 public:
 cppcon_talk(room&&, std::unique_ptr<speaker>, attendees&);
};
```
<!-- .element: style="margin-left:0%; width:105%" -->

```cpp
 Manual DI | [Boost].DI
-------------------------------------+-------------------------------------
 auto room = room{}; |
 auto speaker = |
 std::make_unique<speaker>(); | /*Same as before!*/
 const auto attendees = attendees{}; |
 | auto talk =
 auto talk = cppcon_talk{ | di::create<cppcon_talk>();
 std::move(room), |
 std::move(speaker), |
 attendees}; |
```
<!-- .element: style="margin-left:0%; width:105%" -->

----

### Inject values

```cpp
class attendees {
 public:
 explicit attendees(const std::vector<name>& names) {
 assert(2u == names.size());
 assert("Lenny" == names[0]);
 assert("Shea" == names[1]);
 }
};
```
<!-- .element: style="margin-left:-5%; width:115%" -->

```cpp
 Manual DI | [Boost].DI
------------------------------------+------------------------------------------
 ... |
 std::vector attendees_list = { | auto injector = di::make_injector(
 name{"Lenny"}, name{"Shea"} | ...,
 }; | di::bind<name>.to({name{"Lenny"},
 const auto attendees = | name{"Shea"})
 attendees{attendees_list}; | );
 |
 cppcon_talk talk{std::move(room), | auto talk = injector.create<cppcon_talk>();
 std::move(speaker)|
 attendees); |
```
<!-- .element: style="margin-left:-5%; width:115%" -->

----

### Inject abstractions

```cpp
struct ispeaker {
 virtual ~ispeaker() noexcept = default;
 virtual void present() = 0;
};
struct keynote_speaker : ispeaker;
struct regular_speaker : ispeaker;

struct cppcon_talk {
 cppcon_talk(room&&, std::unique_ptr<ispeaker> speaker, attendees&) {
 assert(dynamic_cast<regular_speaker*>(speaker.get()));
 }
};
```
<!-- .element: style="margin-left:-5%; width:115%" -->

```cpp
 Manual DI | [Boost].DI
-------------------------------------+------------------------------------------
 ... |
 auto speaker = std::make_unique< | auto injector = di::make_injector(
 regular_speaker>(); | ...,
 ... | di::bind<ispeaker>.to<regular_speaker>()
 cppcon_talk talk{std::move(room), | );
 std::move(speaker) | auto talk = injector.create<cppcon_talk>();
 attendees); |
```
<!-- .element: style="margin-left:-5%; width:115%" -->

----

### Inject templates/concepts

```cpp
class Eniac;

template<class TRoom = class Room> // requires RoomLike<TRoom>
class cppcon_talk {
 public:
 cppcon_talk(TRoom&& room, std::unique_ptr<ispeaker>, attendees&);
};
```
<!-- .element: style="margin-left:-5%; width:115%" -->

```cpp
 Manual DI | [Boost].DI
-------------------------------------+------------------------------------------
 auto room = Eniac{}; | auto injector = di::make_injector(
 ... | ...,
 | di::bind<class Room>.to<Eniac>()
 cppcon_talk talk{std::move(room), | );
 std::move(speaker) | auto talk = injector.create<cppcon_talk>();
 attendees); |
```
<!-- .element: style="margin-left:-5%; width:115%" -->

----

### Inject mocks ([GUnit](https://github.com/cpp-testing/GUnit))

```cpp
"should present the talk"_test = [] {
 auto [talk, mocks] = testing::make<cppcon_talk, StrictGMock>();

 EXPECT_CALL(mocks.get<class Room>(), close).WillOnce(Return(true));
 EXPECT_CALL(mocks.get<ispeaker>(), present);

 talk.start();
};
```

----

## Let's inject all the things!

| [Boost].DI | |
| ------- | ------------- |
| Documentation | http://boost-ext.github.io/di |
| Source Code | https://github.com/boost-ext/di |
| Try it online! | http://boost-ext.github.io/di/try_it |
<!-- .element: style="margin-left:-13%; width:125%" -->

-

#### [kris@jusiak.net](mailto:kris@jusiak.net) | [@krisjusiak](https://twitter.com/krisjusiak) | [linkedin.com/in/kris-jusiak](https://www.linkedin.com/in/kris-jusiak)
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