A Few Good Ideas in Programming Languages

A few programming language features that stand out to me are flow typing, memory safety without a garbage collector, the borrow checker, contract programming and asserts.

Flow typing allows a variable to be assigned multiple types throughout its lifetime, similar to dynamic typing but in a statically typed language. This enables the compiler to infer types and provides a dynamic-like experience without sacrificing performance. TypeScript also implements flow typing, while Rust prevents data races through its borrow checker which enforces rules to serialize writes to memory locations.

The borrow checker in Rust guarantees memory safety by enforcing rules such as preventing multiple threads from reading and writing the same memory location simultaneously. By statically preventing data races, Rust eliminates a common class of concurrency bugs.

Contract programming, found in languages like D, allows developers to describe more complex invariants for functions and objects. Asserts are used to check these invariants and trigger errors if violated. D further enhances this with enforce, which throws exceptions for issues outside the program's control, and class-level invariants to maintain object consistency. These features provide a clean and maintainable way to ensure program correctness and consistency.