Sample class to demonstrate usage of `try?` in Swift

TokenGenerator.swift

class TokenGenerator {

  internal struct TokenError: Error {}

  private var canObtainToken = true
  private var token = "TOKEN"

  func obtainToken() throws -> String {
    guard canObtainToken else {
      throw TokenError()
    }

    canObtainToken = false
    return token
  }

  func returnToken() {
    canObtainToken = true
  }
}

let tokenGenerator = TokenGenerator()
let token = try? tokenGenerator.obtainToken()
print(token) // Prints: Optional("TOKEN")

let tokenAgain = try? tokenGenerator.obtainToken()
print(tokenAgain) // Prints: nil