Modules and hooks in Swift


How do modules (plugins) work?

Would not be cool in the event you may create objects that might work collectively with out understanding about one another? Think about that you’re constructing a dynamic kind. Primarily based on some inside circumstances, the fields are going to be composed utilizing the info coming from the enabled modules.

For instance you’ve gotten 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 in the event you flip off B, you need to solely have the ability to see discipline 1, 2, 3 and 6. If every thing is turned on you need to see all of the fields from 1 to six.

We are able to apply this very same sample to many issues. Simply take into consideration one of many largest plugin ecosystem. WordPress is utilizing hooks to increase the core functinalities by way of 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 methodology might be known as by the module supervisor to invoke the correct hook perform by title. We’ll cross round a dictionary of parameters, so our hooks can have arguments. We’re utilizing the Any kind right here as a worth, so you may ship something as a parameter underneath a given key.

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

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

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

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

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

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

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

Subsequent we want a module supervisor that may be initialized with an array of modules. This supervisor might be answerable for calling the best invocation methodology on each single module and it will deal with the returned response in a type-safe method. We’ll implement two invoke methodology variations instantly. One for merging the consequence and the opposite to return the primary results of a hook.

You possibly can 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>(_ title: String, kind: T.Kind, params: [String: Any] = [:]) -> [T] {
        let consequence = self.modules.map { module in
            module.invoke(title: title, params: params)
        }
        return consequence.compactMap { $0 as? [T] }.flatMap { $0 }
    }

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

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

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

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

Utilizing the invokeHook methodology you may obtain an analogous habits just like the chain of duty 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(title: String, params: [String: Any]) -> Any? {
        swap title {
        case "example_form":
            return self.exampleFormHook()
        case "example_responder":
            return self.exampleResponderHook()
        default:
            return nil
        }
    }

    personal func exampleFormHook() -> [String] {
        ["Field 4", "Field 5"]
    }
    
    personal func exampleResponderHook() -> String {
        "Hey, that is module B."
    }
}

If we set off the brand new example_responder hook with the invokeHook methodology on each managers we’ll see that the end result is kind of totally different.

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

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

Within the first case, since we now have an implementation in certainly one of our modules for this hook, the return worth might be current, so we are able to print it. Within the second case there is no such thing as a module to deal with the occasion, so the block contained in the situation will not be executed. Instructed ya’, it is like a responder chain. 😜

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