Generic issue while creating array in Swift

Question

Here is protocol I am using,

public protocol PValidationCondition: Equatable {
    associatedtype T
    func isValid(value: T) -> Bool
    func errorMessage() -> String
}

This is model I am using:

struct PValidationElementWithConditions<T: PValidationCondition> {
    let validationElement: PValidationElement
    var conditions: [T] = []
}

But I would like to store the multiple object in array like the following:

var validationElementsWithConditions: [String: PValidationElementWithConditions] = [:]

But I am getting the following error:

"Cannot convert value of type '[String : PValidationElementWithConditions<_>]' to specified type '[String : PValidationElementWithConditions]'"

you must specify the PValidationElementWithConditions<YourType> type — vivekDas
– vivekDas, Commented Aug 10, 2018 at 13:41

Shehata Gamal · Accepted Answer · 2018-08-10 14:18:30Z

3

This is incorrect

[String: PValidationElementWithConditions]

you have to do

[String: PValidationElementWithConditions<Type>]

where Type conforms to PValidationCondition & Equatable it's clear from the error here that it needs a paramter

PValidationElementWithConditions<_>

//

extension String  : PValidationCondition { 

    public func isValid(value: String) -> Bool {

        return true
    }

    public func errorMessage() -> String {

        return ""
    }

    public typealias T = String 

}

With

var validationElementsWithConditions: [String: PValidationElementWithConditions<String>] = [:]

edited Aug 10, 2018 at 14:18

answered Aug 10, 2018 at 13:41

Shehata Gamal

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6 Comments

Teenenggr Over a year ago

This is not working Cannot convert value of type '[AnyHashable : Any]' to specified type '[String : PValidationElementWithConditions<VComparisionCondition>]'

Teenenggr Over a year ago

This is working but I want to save Int, String or any other object in it(same dict), what should I do in this case?

Shehata Gamal Over a year ago

you can consider them all Strings with interpolation "\(12.5)"

Rob Napier Over a year ago

You cannot use protocols+generics this way. You cannot mix Conditions<String> with Conditions<Int>. You will need to redesign to simplify your types, or you will need to create a boxing struct PValidationElementWithConditions that does not expose its underlying type (and generally also provides no access to it). But I recommend you go back to the problem you're trying to solve and see if you can build it with simpler closures rather than protocols. Protocols are very fragile in Swift, PATs are 100x more fragile.

Rob Napier Over a year ago

The key type issue, though, is if you could do this, how would the compiler be able to deal with validationElementsWithConditions.values.map { $0.conditions }? What type would that return?

|

Abizern · Accepted Answer · 2018-08-10 13:40:16Z

1

Because it's generic, you need to specify the type T in the declaration. For example:

var validationElementsWithConditions: [String: PValidationElementWithConditions<String>] = [:]

answered Aug 10, 2018 at 13:40

Abizern

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3 Comments

Teenenggr Over a year ago

but I want to save Int, String or any other object in it, what should I do in this case?

Teenenggr Over a year ago

open class ParakhValidator { open weak var delegate: PValidatorDelegate? private var validationElementsWithConditions: [String: PValidationElementWithConditions<>] = [:] open static let shared = ParakhValidator() private init() { } }

Teenenggr Over a year ago

this is my class which is singleton

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