The SwiftUIMasonry library provides two custom layout types for SwiftUI: `VMasonry` and `HMasonry`, which arrange subviews in a vertical or horizontal masonry grid respectively. These layouts support adaptive or fixed column/row counts, configurable spacing, and two placement modes (fill or order) to control how subviews are positioned. Subviews can also span multiple columns or rows using the `masonryColumnSpan` and `masonryRowSpan` view modifiers. The library is structured as a Swift package with a clear separation between public API and internal implementation. The API exposes the layout structures, configuration enums (for column/row counts and placement mode), and view extensions for setting span values. The internal files contain the layout logic, including a caching mechanism to optimize performance by storing layout results for specific size proposals. Key reusable components include the `MasonryColumnCount` and `MasonryRowCount` enums, which provide a type-safe way to specify adaptive or fixed dimensions, and the layout value system (keys and view extensions) that allows subviews to communicate their span requirements to the parent layout. These components demonstrate solid SwiftUI engineering practices and could be extracted for use in other custom layout systems.