A Few Good Ideas in Programming Languages

The article highlights three programming language concepts the author admires: Crystal’s flow typing, which tracks variable types across control flow and forces explicit type checks when a variable’s type is a union; Rust’s borrow checker, which statically eliminates data races by allowing either one mutable reference or multiple immutable references within a scope; and D’s contract programming, which distinguishes assertions from enforceable checks and provides built-in pre- and post-condition syntax for functions and objects.