Swift: Swiftの条件分岐：if-elseとswitch文の完全ガイド

if role == "admin" {
    if action == "delete" {
        // allow
    } else if action == "edit" {
        // allow
    }
} else if role == "editor" {
    // 700 lines of repeated code...
}

let role = "editor"
switch role {
case "admin":
    print("Full access granted")
case "editor":
    print("Read and write access")
case "viewer", "guest":
    print("Read-only access")
case "banned":
    print("Access denied")
default:
    print("Unknown role")
}

let temperature = 30
if temperature > 25 {
    print("It's hot outside")
} else {
    print("It's cool outside")
}

let score = 85
if score >= 90 {
    print("Grade: A")
} else if score >= 80 {
    print("Grade: B")
} else if score >= 70 {
    print("Grade: C")
} else if score >= 60 {
    print("Grade: D")
} else {
    print("Grade: F")
}

// ============================================
// Display different messages based on login status
// ============================================
let isLoggedIn = true
let hasProfile = false
if isLoggedIn {
    print("Welcome back!")
    if hasProfile {
        print("Your profile is complete")
    } else {
        print("Please complete your profile")
    }
} else {
    print("Please log in first")
}

let fruit = "apple"
switch fruit {
case "apple":
    print("It's an apple")
case "banana":
    print("It's a banana")
case "orange":
    print("It's an orange")
default:
    print("Unknown fruit")
}

let age = 25
switch age {
case 0..<13:
    print("Child")
case 13..<20:
    print("Teenager")
case 20..<65:
    print("Adult")
case 65...:
    print("Senior")
default:
    print("Invalid age")
}

// ============================================
// Handle HTTP response status codes with switch
// ============================================
let statusCode = 404
switch statusCode {
case 100..<200:
    print("Informational")
case 200..<300:
    print("Success")
case 300..<400:
    print("Redirection")
case 400..<500:
    print("Client error")
    if statusCode == 404 {
        print("Resource not found")
    }
case 500..<600:
    print("Server error")
default:
    print("Unknown status code")
}

let number = 2
switch number {
case 1:
    print("One")
case 2:
    print("Two")
    fallthrough
case 3:
    print("Three or fell through from two")
default:
    print("Other")
}

let point = (x: 3, y: 4)
switch point {
case let (x, y) where x == y:
    print("On the diagonal")
case let (x, y) where x > y:
    print("X is larger")
case let (x, y) where x < y:
    print("Y is larger")
default:
    print("On an axis")
}

let isMember = true
let discount = isMember ? 0.2 : 0.0
print("Discount: \(discount * 100)%")

// ============================================
// Combine if/switch/ternary to calculate order discounts
// ============================================
let orderTotal = 250.0
let customerTier = "gold"
// Ternary operator: base discount
let baseDiscount = orderTotal > 100 ? 0.05 : 0.0
// switch: membership tier discount
let tierDiscount: Double
switch customerTier {
case "platinum":
    tierDiscount = 0.20
case "gold":
    tierDiscount = 0.15
case "silver":
    tierDiscount = 0.10
default:
    tierDiscount = 0.0
}
// if: cap the combined discount
let totalDiscount = baseDiscount + tierDiscount
let finalDiscount = totalDiscount > 0.3 ? 0.3 : totalDiscount
let finalPrice = orderTotal * (1 - finalDiscount)
print("Order total: $\(orderTotal)")
print("Tier: \(customerTier)")
print("Discount: \(Int(finalDiscount * 100))%")
print("Final price: $\(finalPrice)")

// ============================================
// User permission management system
// Integrates if/switch/where/ternary operators
// ============================================
import Foundation
enum UserRole {
    case admin, editor, viewer, guest, banned
}
enum ActionResult {
    case granted, denied(String)
}
func checkPermission(role: UserRole, action: String, isOwner: Bool) -> ActionResult {
    switch role {
    case .banned:
        return .denied("Account is banned")
    case .admin:
        return .granted
    case .editor:
        if action == "delete" && !isOwner {
            return .denied("Only owners can delete")
        }
        return .granted
    case .viewer:
        switch (action, isOwner) {
        case (_, false):
            return .denied("Viewers cannot modify content")
        case ("read", true):
            return .granted
        default:
            return .denied("Unknown action")
        }
    case .guest:
        return action == "read" ? .granted : .denied("Guests can only read")
    }
}
let testCases = [
    (UserRole.admin, "delete", false),
    (UserRole.editor, "delete", true),
    (UserRole.editor, "delete", false),
    (UserRole.viewer, "read", true),
    (UserRole.viewer, "write", false),
    (UserRole.guest, "read", false),
    (UserRole.banned, "read", false)
]
for (role, action, isOwner) in testCases {
    let result = checkPermission(role: role, action: action, isOwner: isOwner)
    switch result {
    case .granted:
        print("[GRANTED] \(role) can \(action)")
    case .denied(let reason):
        print("[DENIED] \(role) cannot \(action) -- \(reason)")
    }
}