Module Docs

Overview

LibJuno implements dependency injection through modules and API traits. This is very similar to the Rust paradigm. There are 3 components to modules within LibJuno:

• The module
• The module root
• The module derivations

The Module Root

Before talking about the module itself we need to go over the module root.

• The module root is a common set of member variables shared across all module derivations and implementations.
• When a module is derived there is a compile-time gurantee that the module can be safely up-cast to the module root.
  • All derivations of the module can up-cast to the module root.
• The module root always provides the following as defined by the macros:
  • ptApi – A pointer to the API traits
  • _pfcnFailureHandler – A failure handler callback
  • _pvFailurUserData – User defined data pointer to provide to the failure handler callback
• Members within the module root should be freestanding
  • The real power within DI is to isolate dependencies
  • The module root should not contain any dependencies. Ideally the module root should only contain types supported by your freestanding C standard, like C99 or C11. This enables highly portable modules.
  • Implementation details and dependencies belong in the module derivations

Implementing a Module: Derivations

• Concrete implementations for a module are created through deriving the module.
• A derivation is guranteed to have the module root as the the first member. Module derivations can always be safely up-cast to the module root.
• The module derivations can contain implementation specific details, dependencies, and other private memebers.
• You can think of the members placed within the derivation as "private" in C++ terms

The Module

Now with a background on the module root and module derivations, we can talk about the module.

• The module is a union of all possible derivations, including the root.
• The module is forward-declared. Module implementations will provide a default implementation of the module that can be overridden when ..._CUSTOM is defined.
  • The user of the module would define ..._CUSTOM if they want polymorphic behavior.
• API traits are provided a pointer to the module.

How to Define The Module Union

Below is an example of defining a module union:

union MY_MODULE_T JUNO_MODULE(MY_MODULE_API_T, MY_MODULE_ROOT_T,
    MY_MODULE_DERIVATION_1_T;
    MY_MODULE_DERIVATION_2_T;
    MY_MODULE_DERIVATION_3_T;
);