A retrospective on years of contributions to PHPStan's type inference engine, focusing on handling mixed types. Covers improvements to type narrowing from conditionals, type casts, and comparisons; support for immediately-invoked function expressions; new PHPDoc types like non-falsy-string and @param-out; and advanced type inference for regex patterns, printf functions, and database queries through AST analysis. Demonstrates how subtractable types help narrow down unknowns by eliminating what types cannot be.
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