Choose efficient data structures

Select data structures and algorithms based on their performance characteristics and expected usage patterns. Consider the size of collections, access patterns, and computational complexity when making implementation choices.

Key considerations:

• Use HashSet instead of Vec for membership testing when collections can be large
• Choose data structures that preserve order when sequence matters (e.g., IndexMap vs HashMap)
• Prefer more efficient algorithms when available (e.g., checking if a commit is a head vs. evaluating all children)
• Combine operations to reduce computational overhead (e.g., union revset expressions rather than evaluating separately)

Example:

// Instead of Vec for large collections with frequent lookups
let already_tracked_bookmarks: Vec<String> = ...;
if already_tracked_bookmarks.contains(&bookmark) { ... } // O(n) lookup

// Use HashSet for O(1) average lookup time
let already_tracked_bookmarks: HashSet<String> = ...;
if already_tracked_bookmarks.contains(&bookmark) { ... } // O(1) lookup

This applies especially when dealing with user-facing operations that may scale with repository size or when processing large collections where the choice of data structure significantly impacts performance.