Introduced by Chris Lattner at Apple in 2014, Swift combines the raw performance of compiled C with the expressive clarity of modern languages. Swift 6 enforces Complete Data-Race Safety at compile time:

import Foundation

// Immutable Struct: Value Type with automatic memberwise initializer
public struct StockQuote: Identifiable, Sendable {
    public let id: UUID
    public let symbol: String
    public let price: Decimal
    public let timestamp: Date

    public init(symbol: String, price: Decimal) {
        self.id = UUID()
        self.symbol = symbol
        self.price = price
        self.timestamp = Date()
    }
}

// Swift 6 Typed Throws Architecture
enum OrderError: Error {
    case marketClosed
    case insufficientFunds(shortfall: Decimal)
}

func submitOrder(quote: StockQuote, shares: Int) throws(OrderError) -> String {
    guard shares > 0 else { throw OrderError.marketClosed }
    return "Successfully routed order for (shares) shares of (quote.symbol)"
}

An actor serializes access to its internal mutable state, eliminating data races without manual mutex locking. @MainActor guarantees execution on the iOS main thread.

SwiftUI uses AttributeGraph: a high-performance directed acyclic graph that tracks property dependencies at the field level, executing minimal UI node invalidations with zero manual diffing.

Prefer some Protocol (Opaque Return Types with compile-time monomorphization) over any Protocol (Existential containers with dynamic witness table dispatch overhead).

SwiftData replaces legacy Core Data XML models with clean Swift macros (@Model, @Query), supporting actor-isolated background model context operations.

Stream large multi-gigabyte files asynchronously with minimal memory pressure using URLSession.shared.bytes(for: request).

Manage large-scale iOS applications using Unidirectional Data Flow (UDF) with Point-Free's Composable Architecture (TCA) and modular SPM packages.

Generate non-exportable hardware private keys inside the Apple Secure Enclave (TEE) and perform AES-GCM encryption with CryptoKit.

Diagnose UI scroll hitch rates using Xcode Instruments to maintain a flawless 120fps ProMotion refresh rate without dropping frames.