One of Swift's smartest optimizations is also one of its most misunderstood. When you write: var array2 = array1 Swift usually doesn't copy the data immediately. Instead, it uses Copy-on-Write (CoW) and delays the copy until a mutation occurs. This gives us: Value semantics Memory efficiency Better performance Safer code Understanding CoW explains why Swift collections like Array, Dictionary, and Set are both fast and safe. I recently explored how CoW works under the hood and why it matters for