CodableDashCase.swift

import Foundation

struct AnyKey: CodingKey {
    var stringValue: String
    var intValue: Int?
    
    init?(stringValue: String) {
        self.stringValue = stringValue
        self.intValue = nil
    }
    
    init?(intValue: Int) {
        self.stringValue = String(intValue)
        self.intValue = intValue
    }
}

func convertFromDashCase(_ keys: [CodingKey]) -> CodingKey {
    var key = keys.last?.stringValue ?? ""
    var parts = key.split(separator: "-").compactMap(String.init)
    
    guard parts.count > 1 else {
        return AnyKey(stringValue: key)!
    }

    for (index, part) in parts.enumerated() {
        if index != 0 { parts[index] = part.capitalized }
    }

    key = parts.joined()
    return AnyKey(stringValue: key)!
}

let JSON = """
{
    "title": "A weekly Swift Blog on Xcode and iOS Development - SwiftLee",
    "url": "https://www.avanderlee.com",
    "total-visitors": 378483,
    "number-of-posts": 47093
}
"""

let jsonData = JSON.data(using: .utf8)!

struct Blog: Decodable {
    let title: String
    let url: URL
    let totalVisitors: Int
    let numberOfPosts: Int
}

let decoder = JSONDecoder()
decoder.keyDecodingStrategy = .custom(convertFromDashCase(_:))

let blog: Blog = try! decoder.decode(Blog.self, from: jsonData)
print(blog.numberOfPosts) // Prints: 47093