rust

The borrow checker rejects some correct programs, so Rust provides ways out: runtime-checked cells, reference counting, and unsafe blocks. This lesson covers what each escape hatch turns off, what it does not, and the encapsulation discipline that keeps a small unsafe core from voiding the guarantee for everything above it.

Rust did not add a concurrency safety mechanism. A data race requires aliasing plus mutation, which the borrow checker already forbids, so data races became compile errors as a side effect. This lesson shows how two marker traits extend that guarantee across threads, and what it still does not prevent.

Moving a value to read it is unusable, so ownership needs a way to lend. The lending rule is one line, and it is the reason Rust can guarantee no dangling references: you may have many readers or one writer, never both. This lesson builds that rule and the lifetimes that enforce it across function boundaries.

Every language must decide who frees memory and when. Rust answers with a rule enforced at compile time: each value has exactly one owner, and it is freed when that owner goes out of scope. This lesson builds the rule, shows what moving a value means, and explains what the approach buys and charges.