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https://github.com/phs/sauce

A C++98 Dependency Injection Framework MOVED TO GITLAB
https://github.com/phs/sauce

c-plus-plus dependency-injection

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A C++98 Dependency Injection Framework MOVED TO GITLAB

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README 

        
# Sauce #



[![Linux and OS X Build Status][travis-badge]][travis]



[travis-badge]: https://travis-ci.org/phs/sauce.png?branch=master

[travis]: https://travis-ci.org/phs/sauce



A *C++98* dependency injection framework.



If you do not need strict C++98 compatibility, I suggest you look at Google's

[fruit][google-fruit] instead.



The design and name are inspired by Google's excellent [Guice framework][google-guice],

but neither Google nor Guice is otherwise affiliated in any way.



[google-guice]: https://github.com/google/guice

[google-fruit]: https://github.com/google/fruit



## The Gist ##



I refer the reader to [Guice's documentation][guice-motivation] for an introduction to

dependency injection as a concept, and why they might be interested in using it.



In Sauce, one defines _bindings_ that map interface types to implementation types.  Each

binding is declared in the context of a _module_ which is used to organize and refer to

collections of bindings at a time.  Modules may be function pointers, or classes

providing a certain `operator()`.  Groups of modules may be used together, to avoid

duplicate bindings.



At runtime, one collects desired modules into a _modules_ object, which produces

_injectors_.  One can then ask an injector to _provide_ a value (instance) of a desired

type (again supplied as a template parameter.)  When providing a value, implicit

transitive dependencies are provided as well.  All values are exchanged with shared

pointers (`(std|std::tr1|boost)::shared_ptr`s are supported) and the injector takes care

of _disposing_ the value when the smart pointer deletes itself.



Requesting the injector for an unbound type results in a runtime exception.  No RTTI is

used (but we use a portable, homebrew version of same.)



Sauce is available with a liberal, BSD-ish [license][sauce-license].



[guice-motivation]: https://github.com/google/guice/wiki/Motivation

[sauce-license]: https://github.com/phs/sauce/blob/master/LICENSE



## Hacking ##



Development that is not environment-specific is done with [vagrant][vagrant] over

[virtualbox][virtualbox]:



```bash

$ vagrant up

$ vagrant ssh

vagrant@sauce:~$ cd sauce

vagrant@sauce:~/sauce$ ./configure  # create make files

vagrant@sauce:~/sauce$ make check   # compile and run unit tests

```



[vagrant]: http://www.vagrantup.com/

[virtualbox]: https://www.virtualbox.org/



## Scopes ##



A side-effect of using an injector to hide implementation choices from dependents is the

discouraged use of stack allocation and the `new` operator for dependencies.  The `new`

operator (et. al.) has an additional guarantee past the ensuring the instance's concrete

type: the instance received is unique, and not shared.  This raises the question: will

the injector always provide new, successive instances, or will it ever reuse some?



It turns out the most useful answer is "both".  Depending on the context, it may be

appropriate to always create new instances upon request, to always share a solitary

instance with everyone (such as in the [_Singleton_][singleton] pattern), or to do

something in between.



Sauce supports _scopes_ to answer this need.  While within a scope, a participating

binding will only ever create a single instance of its bound type: if the dependency is

provided more than once, the same instance is reused.  One enters a scope with the

`enter` method on the injector, to receive a _scoped_ injector.  Requests made to this

injector will benefit from the open scope.  To leave the scope, stop using the scoped

injector (either by simply dropping it on the floor, or by calling `exit` to recover the

original.)  The injectors returned from `Modules` instances are created implicitly in

`SingletonScope`, which can not be exited (at pain of runtime exception.)



Entered scopes form a stack: entering the `RequestScope` from a `SessionScope` injector

will result in an injector that is within both scopes.  Put differently, such an injector

will try to provide both `RequestScope` and `SessionScope` dependencies from cache.  They

are a stack in the sense that injectors beneath the top are guaranteed to survive those

above them.  It is illegal to reenter a scope already on the stack; a runtime exception

is thrown.



It is possible (and encouraged!) to reenter a scope many times from a single injector in

_parallel_.  For example, one may enter `RequestScope` from the same `SessionScope`

injector many times concurrently, to create many contemporary `RequestScope` injectors.

These will all cache `RequestScope` dependencies separately, but share the same

`SessionScope` cache.  Such shared scopes are not thread-safe by default, but may be made

so by supplying a locker type and a lockable instance when creating the initial, root

injector.  [Boost::thread][boost-thread]'s [`lock_guard`][boost-lock-guard] and

[`mutex`][boost-mutex] are suitable for this purpose.



Sometimes it is convenient to force the creation of all dependencies up front in a given

scope (such as singleton scope.)  This can help programs fail fast, by exposing

environmental issues or other problems at start up.  Sauce supports this by optionally

_eagerly injecting_ arbitrary scopes (with an injector method.)  One may only eagerly

inject dependencies in open scopes.



Unlike Guice, Sauce expects the developer to enter and eagerly inject scopes explicitly,

at their convenience.  No entrance or eager injection occurs implicitly.



[singleton]: http://en.wikipedia.org/wiki/Singleton_pattern

[boost-thread]: http://www.boost.org/doc/libs/1_47_0/doc/html/thread.html

[boost-lock-guard]: http://www.boost.org/doc/libs/1_47_0/doc/html/thread/synchronization.html#thread.synchronization.locks.lock_guard

[boost-mutex]: http://www.boost.org/doc/libs/1_47_0/doc/html/thread/synchronization.html#thread.synchronization.mutex_types.mutex



## Further Reading ##



* [The "Tutorial" Test Suite](https://github.com/phs/sauce/blob/master/test/tutorial_test.cc)

* [API Reference](http://phs.github.com/sauce/doxygen-doc/html/)



## Wishlist ##



* ~~Circular dependency detection~~

* ~~Setter injection~~

* ~~Named, overloaded bindings~~

* ~~Eager-loaded singletons~~

* ~~Injectable Providers for lazy resolution~~

* Implicit bindings implied by integration within interfaces or implementations

* ~~On-demand injection for provided instances~~

* Member field injection (meh)

* Static injection (meh)



## Thanks ##



These peeps are amaze for helping make Sauce better!  Buy them all the drink of their

choice!



* Casey B.

* Jakub S.

* Markus E.

* [smithgeek](https://github.com/smithgeek)



(If you're up here and want me to tweak/link, make a ticket or otherwise prod me.)



## Copyright ##



Copyright (c) 2011-2017 Phil Smith. See LICENSE for details.