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Adding Assembler feature for modular components
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mike.owens
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Dec 10, 2015
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| # Modularizing Service Registration | ||
| This feature provides your implementation the ability to group related service definitions together | ||
| in an `AssemblyType`. This allows your application to: | ||
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| - keep things organized by keeping like services in 1 place | ||
| - provided a shared `Container` | ||
| - allows registering different assembly configurations which is useful for swapping out mock implementations | ||
| - can be "load aware" when the container is fully configured | ||
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| This feature is an opinionated way to how your can register services in your `Container`. There are | ||
| parts to this feature: | ||
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| ## AssemblyType | ||
| The `AssemblyType` is a protocol that is provided a shared `Container` where service definitions | ||
| can be registered. The shared `Container` will contain **all** service definitions from every | ||
| `AssemblyType` registered to the `Assembler`. Let's look at an example: | ||
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| class ServiceAssembly: AssemblyType { | ||
| func assemble(container: Container) { | ||
| container.register(FooServiceType.self) { r in | ||
| return FooService() | ||
| } | ||
| container.register(BarServiceType.self) { r in | ||
| return BarService() | ||
| } | ||
| } | ||
| } | ||
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| class ManagerAssembly: AssemblyType { | ||
| func assemble(container: Container) { | ||
| container.register(FooManagerType.self) { r in | ||
| return FooManager(service: r.resolve(FooServiceType.self)!) | ||
| } | ||
| container.register(BarManagerType.self) { r in | ||
| return BarManager(service: r.resolve(BarServiceType.self)!) | ||
| } | ||
| } | ||
| } | ||
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| Here we have created 2 assemblies: 1 for services and 1 for managers. As you can see the `ManagerAssembly` | ||
| leverages service definitions registered in the `ServiceAssembly`. Using this pattern the `ManagerAssembly` | ||
| doesn't care where the `FooServiceType` and `BarServiceType` are registered, it just requires them to | ||
| be registered else where. | ||
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| ### AssemblyLoadAwareType | ||
| The `AssemblyLoadAwareType` supports the assembly to be aware when the container has been fully loaded | ||
| by the `Assembler`. | ||
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| Let's imagine you have an simple Logger class that can be configured with different log handlers: | ||
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| protocol LogHandlerType { | ||
| func log(message: String) | ||
| } | ||
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| class Logger { | ||
| class var sharedInstance: Logger! | ||
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| var logHandlers = [LogHandlerType]() | ||
| func addHandler(logHandler: LogHandlerType) { | ||
| logHandlers.append(logHandler) | ||
| } | ||
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| func log(message: String) { | ||
| for logHandler in logHandlers { | ||
| logHandler.log(message) | ||
| } | ||
| } | ||
| } | ||
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| This singleton is accessed in global logging functions to make it easy to add logging anywhere | ||
| without having to deal with injects: | ||
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| func logDebug(message: String) { | ||
| Logger.sharedInstance.log("DEBUG: \(message") | ||
| } | ||
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| In order to configure the `Logger` shared instance in the container we will need to resolve the | ||
| `Logger` after the `Container` has been built. Using a `AssemblyLoadAwareType` you can keep this | ||
| bootstrapping in the assembly: | ||
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| class LoggerAssembly: AssemblyLoadAwareType { | ||
| func assemble(container: Container) { | ||
| container.register(LogHandlerType.self, name: "console") { r in | ||
| return ConsoleLogHandler() | ||
| } | ||
| container.register(LogHandlerType.self, name: "file") { r in | ||
| return FileLogHandler() | ||
| } | ||
| } | ||
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| func loaded(resolver: ResolverType) { | ||
| Logger.sharedInstance.addHandler( | ||
| resolver.resolve(LogHandlerType.self, name: "console")!) | ||
| Logger.sharedInstance.addHandler( | ||
| resolver.resolve(LogHandlerType.self, name: "file")!) | ||
| } | ||
| } | ||
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| ## Assembler | ||
| The `Assembler` is responsible for managing the `AssemblyType` instances and the `Container`. Using | ||
| the `Assembler` the `Container` is only exposed to assemblies registered with the assembler and | ||
| only provides your application access via the `ResolverType` protocol which limits registration | ||
| access strictly to the assemblies. | ||
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| Using the `ServiceAssembly` and `ManagerAssembly` above we can create our assembler: | ||
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| let assembler = try! Assembler(assemblies: [ | ||
| ServiceAssembly(), | ||
| ManagerAssembly() | ||
| ]) | ||
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| Now you can resolve any components from either assembly: | ||
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| let fooManager = assembler.resolver.resolve(FooManagerType.self)! | ||
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| You can also lazy load assemblies: | ||
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| assembler.applyAssembly(LoggerAssembly()) | ||
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| The assembler also supports managing your property files as well via construction or lazy loading: | ||
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| let assembler = try! Assembler(assemblies: [ | ||
| ServiceAssembly(), | ||
| ManagerAssembly() | ||
| ], propertyLoaders: [ | ||
| JsonPropertyLoader(bundle: .mainBundle(), name: "properties") | ||
| ]) | ||
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| // or lazy load them | ||
| assembler.applyPropertyLoader( | ||
| JsonPropertyLoader(bundle: .mainBundle(), name: "properties")) | ||
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| ## IMPORTANT: | ||
| - You **MUST** hold a strong reference to the `Assembler` otherwise the `Container` | ||
| will be deallocated along with your assembler | ||
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| - If you are lazy loading your properties and assemblies you must load your properties **first** if | ||
| you want your properties to be available to load aware assemblies when `loaded` is called | ||
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| - If you are lazy loading assemblies and you want your load aware assemblies to be invoked after | ||
| all assemblies have been loaded then you must use `addAssemblies` and pass all lazy loaded assemblies | ||
| at once | ||
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| _[Table of Contents](README.md)_ |
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