Modules and hooks in Swift

How do modules (plugins) work?

Would not be cool for those who may create objects that would work collectively with out realizing about one another? Think about that you’re constructing a dynamic type. Primarily based on some inside situations, the fields are going to be composed utilizing the info coming from the enabled modules.

For instance you’ve module A, B, C, the place A is offering you Discipline 1, 2, 3, the B module is taking good care of Discipline 4, 5 and C is the supplier of Discipline 6. Now for those who flip off B, you need to solely be capable of see subject 1, 2, 3 and 6. If all the things is turned on you need to see all of the fields from 1 to six.

We will apply this very same sample to many issues. Simply take into consideration one of many greatest plugin ecosystem. WordPress is utilizing hooks to increase the core functinalities via them. It is all based mostly on the idea I simply talked about above. That is a part of the event-driven structure design sample. Now the query is how will we implement one thing related utilizing Swift? 🤔

A hook system implementation

First we begin with a protocol with some extent of invocation. This technique shall be referred to as by the module supervisor to invoke the right hook perform by identify. We will go round a dictionary of parameters, so our hooks can have arguments. We’re utilizing the Any sort right here as a worth, so you may ship something as a parameter below a given key.

protocol Module {
    func invoke(identify: String, params: [String: Any]) -> Any?
}

extension Module {
    func invoke(identify: String, params: [String: Any]) -> Any? { nil }
}

Now let’s implement our modules utilizing a simplified model based mostly on the shape instance. 🤓

class A: Module {

    func invoke(identify: String, params: [String: Any]) -> Any? {
        swap identify {
        case "example_form":
            return self.exampleFormHook()
        default:
            return nil
        }
    }

    non-public func exampleFormHook() -> [String] {
        ["Field 1", "Field 2", "Field 3"]
    }
}

class B: Module {
    func invoke(identify: String, params: [String: Any]) -> Any? {
        swap identify {
        case "example_form":
            return self.exampleFormHook()
        default:
            return nil
        }
    }

    non-public func exampleFormHook() -> [String] {
        ["Field 4", "Field 5"]
    }
}

class C: Module {
    func invoke(identify: String, params: [String: Any]) -> Any? {
        swap identify {
        case "example_form":
            return self.exampleFormHook()
        default:
            return nil
        }
    }

    non-public func exampleFormHook() -> [String] {
        ["Field 6"]
    }
}

Subsequent we’d like a module supervisor that may be initialized with an array of modules. This supervisor shall be liable for calling the precise invocation technique on each single module and it will deal with the returned response in a type-safe method. We will implement two invoke technique variations immediately. One for merging the end result and the opposite to return the primary results of a hook.

You’ll be able to attempt to implement a model that may merge Bool values utilizing the && operator

Right here is our module supervisor implementation with the 2 generic strategies:

struct ModuleManager {

    let  modules: [Module]
    
    func invokeAllHooks<T>(_ identify: String, sort: T.Kind, params: [String: Any] = [:]) -> [T] {
        let end result = self.modules.map { module in
            module.invoke(identify: identify, params: params)
        }
        return end result.compactMap { $0 as? [T] }.flatMap { $0 }
    }

    func invokeHook<T>(_ identify: String, sort: T.Kind, params: [String: Any] = [:]) -> T? {
        for module in self.modules {
            let end result = module.invoke(identify: identify, params: params)
            if end result != nil {
                return end result as? T
            }
        }
        return nil
    }
}

You should utilize the the invokeAllHooks technique to merge collectively an array of a generic sort. That is the one which we are able to use to assemble all he type fields utilizing the underlying hook strategies.

let manager1 = ModuleManager(modules: [A(), B(), C()])
let form1 = manager1.invokeAllHooks("example_form", sort: String.self)
print(form1) 

let manager2 = ModuleManager(modules: [A(), C()])
let form2 = manager2.invokeAllHooks("example_form", sort: String.self)
print(form2) 

Utilizing the invokeHook technique you may obtain an identical habits just like the chain of accountability design sample. The responder chain works very related similiar, Apple makes use of responders on virtually each platform to deal with UI occasions. Let me present you the way it works by updating module B. 🐝

class B: Module {
    func invoke(identify: String, params: [String: Any]) -> Any? {
        swap identify {
        case "example_form":
            return self.exampleFormHook()
        case "example_responder":
            return self.exampleResponderHook()
        default:
            return nil
        }
    }

    non-public func exampleFormHook() -> [String] {
        ["Field 4", "Field 5"]
    }
    
    non-public func exampleResponderHook() -> String {
        "Hi there, that is module B."
    }
}

If we set off the brand new example_responder hook with the invokeHook technique on each managers we’ll see that the result is sort of completely different.

if let worth = manager1.invokeHook("example_responder", sort: String.self) {
    print(worth) 
}

if let worth = manager2.invokeHook("example_responder", sort: String.self) {
    print(worth) 
}

Within the first case, since now we have an implementation in one in all our modules for this hook, the return worth shall be current, so we are able to print it. Within the second case there isn’t a module to deal with the occasion, so the block contained in the situation will not be executed. Advised ya’, it is like a responder chain. 😜