How Rust Closures Work: Compiler-Generated Types and Capture Traits

The article explains that Rust closures were introduced because standard function pointers cannot capture variables from their surrounding scope. It describes closures as compiler-generated, anonymous types that store captured variables in internal fields. The compiler implements the Fn, FnMut, or FnOnce trait depending on whether captured values are borrowed immutably, borrowed mutably, or consumed. The author notes that the move keyword is often needed to satisfy lifetime rules, such as when spawning threads or returning closures from functions.