Correct use of Go's built-in data structures: slices (nil vs empty, append semantics, aliasing, preallocation), maps (comma-ok, sets, iteration order), arrays, and choosing between them. Use when: "slice vs array", "nil slice", "empty slice", "preallocate", "map iteration", "use a set in Go", "slice aliasing", "append gotcha", "copy a slice", "sync.Map or mutex". Not for: structures shared across goroutines (go-concurrency-review), allocation profiling (go-performance-review), generic containers (go-design-patterns).
