Swift Reference

// print adds a newline
print("Hello, World!")

# Run as script
swift main.swift

# Compile to binary
swiftc main.swift -o main
./main

// Single-line comment

/* Multi-line
   comment */

/// Documentation comment

import Foundation
import Network
import SQLite3

import Foundation

// Exit with status 1
exit(1)

enum MyError: Error { case failure }

func task() throws { throw MyError.failure }

do {
    try task()
} catch {
    print("Caught: \(error)")
}

let constant = 10  // Immutable
var mutable = 20   // Mutable
let typed: Int = 5 // Explicit type

let i: Int = 100       // Platform dependent width
let i64: Int64 = 1000  // Explicit 64-bit
let u8: UInt8 = 255    // Unsigned 8-bit

let s = "123"
let i = Int(s) // Optional(123)
let d = Double(i ?? 0)

// Type casting
let val: Any = "Hello"
let str = val as? String

let x = 1
if x != 0 { print("True") }

import Foundation

let path = ProcessInfo.processInfo.environment["PATH"]

import Foundation

let now = Date()
let formatter = ISO8601DateFormatter()
print(formatter.string(from: now))

// Monotonic clock (Swift 5.7+)
let clock = ContinuousClock()
let elapsed = clock.measure { /* work */ }

let a = 10 / 3 // 3
let b = 10.0 / 3.0 // 3.333...
let c = true && false
let d = !true

import Foundation

// Modern Regex (Swift 5.7+)
let regex = /\d+/
if let match = "price: 100".firstMatch(of: regex) {
    print(match.0)
}

import Foundation

let args = CommandLine.arguments
if args.count > 1 {
    print("First arg: \(args[1])")
}

func add(a: Int, b: Int = 0) -> Int {
    return a + b
}

// Multi-return via Tuple
func getStatus() -> (Int, String) {
    return (200, "OK")
}

class Person { var name = "" }
struct Point { var x = 0 }

// Manual memory (rarely needed)
let ptr = UnsafeMutablePointer<Int>.allocate(capacity: 1)
ptr.pointee = 42
ptr.deallocate()

for i in 1...3 { print(i) } // 1, 2, 3
for i in 0..<3 { print(i) } // 0, 1, 2

var x = 0
while x < 2 { x += 1 }

for i in 1...5 {
    if i == 2 { continue }
    if i == 4 { break }
    print(i)
}

let list = ["a", "b"]
for (index, val) in list.enumerated() {
    print("\(index): \(val)")
}

let s = "  hello  "
let trimmed = s.trimmingCharacters(in: .whitespaces)
let upper = trimmed.uppercased()
let joined = ["a", "b"].joined(separator: "-")

import Foundation

let url = URL(fileURLWithPath: "/tmp").appendingPathComponent("test.txt")
print(url.path)

import Foundation

if let handle = FileHandle(forReadingAtPath: "data.bin") {
    defer { handle.closeFile() }
    while let chunk = try? handle.read(upToCount: 4096), !chunk.isEmpty {
        // Process Data chunk
    }
}

import Foundation

let content = try? String(contentsOfFile: "file.txt", encoding: .utf8)
let data = try? Data(contentsOf: URL(fileURLWithPath: "file.txt"))

import Foundation

var data = Data(count: 12)
var val: Int32 = 42
withUnsafeBytes(of: val) { data.replaceSubrange(0..<4, with: $0) }

let a = 0b1010 & 0b1100 // 0b1000
let b = 0b1010 | 0b1100 // 0b1110
let c = 1 << 3          // 8

let hex = String(255, radix: 16) // "ff"
let val = Int("ff", radix: 16)   // 255

let arr = [1, 2]                 // Array
let dict = ["k": "v"]            // Dictionary
let set: Set = [1, 2, 2]         // Set {1, 2}

import Foundation

struct User: Codable { let id: Int }
let json = "{\"id\": 42}".data(using: .utf8)!
let user = try? JSONDecoder().decode(User.self, from: json)

import Network

let conn = NWConnection(host: "example.com", port: 80, using: .tcp)
conn.start(queue: .main)
conn.send(content: "GET / HTTP/1.0\r\n\r\n".data(using: .utf8), completion: .contentProcessed({ _ in }))

import Network

let conn = NWConnection(host: "127.0.0.1", port: 8080, using: .udp)
conn.start(queue: .main)

import Foundation

// GCD
DispatchQueue.global().async {
    print("In background")
}

// Swift Concurrency (async/await)
Task {
    print("In Task")
}

import SQLite3

var db: OpaquePointer?
sqlite3_open(":memory:", &db)
sqlite3_exec(db, "CREATE TABLE t(id INT)", nil, nil, nil)
sqlite3_close(db)