====== Programming language design ======


===== Value semantics =====

E.g. Swift:

Many references to one variable.

  * In Python: Reference semantics. Defensive copies => clone with bad performance
  * In Swift: Value semantics. **Copy on write.** Only one reference => in-place update.
  * In Java: Immutable strings. Also in functional languages. Safe, but expensive.

===== Progressive disclosure of complexity =====