Select between sequence and non-sequence generic functions in struct-CodePudding

I have a struct that can take in both sequences of values and scalar values (numbers/strings/booleans) as its generic type. I'd like for them to be described by two different functions without having to do any type checking at runtime. I tried using generics but it didn't quite work :

import Foundation

struct Box<T>: CustomStringConvertible {
    static func descriptor<T: Sequence>(box: Box<T>) -> String {
        return "This is a vector Box"
    }
    
    static func descriptor<T>(box: Box<T>) -> String {
        return "This is a scalar Box"
    }
    
    var description: String {
        return Box<T>.descriptor(box: self)
    }
}

let b = Box<Double>()
b.description                              // "This is a scalar Box"
let c = Box<[Double]>()
c.description                              // "This is a scalar Box"

Expected to get "This is a vector Box" for the second call.

I also tried constraining the generic of the first function to be of type Collection but got the same result.

CodePudding user response：

One possibility is to provide two description methods, where the second is defined in a type-constrained extension:

struct Box<T>: CustomStringConvertible {
    var description: String {
        return "This is a scalar Box"
    }
}

extension Box where T: Sequence {
    var description: String {
        return "This is a vector Box"
    }
}

let b = Box<Double>()
print(b.description)    // "This is a scalar Box"
let c = Box<[Double]>()
print(c.description)    // "This is a vector Box"