strong-types

Write, edit, and review code so every value has one knowable type at every point in the program. Type ambiguity is a defect: if the author cannot say what type an expression is without running the code, the code is not done.

Passive Trigger

Load this skill in the background whenever a coding task touches a language with a real type system — static (C#, Java, Kotlin, Swift, Go, Rust, TypeScript) or gradual with mature tooling (PHP, Python, Ruby with Sorbet, Elixir with typespecs). Apply it to new code, edits, refactors, reviews, and implementation plans alike.

Keep it proportional: for small edits, run a silent type-ambiguity pass and mention only the decisions that change the implementation. Also load {{ skill:maintainable-code }} for general code quality when available. When the language or codebase has no usable type system, read references/gradual-languages.md and do not force the issue.

The Canonical Offense

$image = $location->preview ?? $location->banner ?? $location->thumbnail;

This line encodes four unanswered questions: what type is each property, which of them are nullable and why, what type is $image afterward, and can the whole chain still be null. Strongly typed code answers all four in the signature: