geometry_trait/
collection.rs

1//! The [`GeometryCollection`] concept — a sequence of geometries.
2//!
3//! Mirrors `boost::geometry::model::geometry_collection` in
4//! `boost/geometry/geometries/geometry_collection.hpp` and the
5//! `geometry_collection_tag` marker in
6//! `boost/geometry/core/tags.hpp` (`struct geometry_collection_tag :
7//! multi_tag {};`). The C++ model derives from
8//! `Container<DynamicGeometry, Allocator<DynamicGeometry>>` and is
9//! consumed through `boost::range`; this Rust port surfaces the
10//! element sequence via an RPITIT `items()` iterator, matching the
11//! pattern already used by the multi-* traits.
12//!
13//! **Scope:** v1 only supplies the trait surface. Heterogeneous
14//! dynamic dispatch (a `dyn`/`enum`-based story that would let one
15//! collection mix Points, Linestrings, Polygons, …) is intentionally
16//! deferred — see `specs/FUTURE_ITERATIONS.md` §1.3 (`DynGeometry`
17//! variant) and §1.4 (heterogeneous `GeometryCollection`). The
18//! [`GeometryCollection::Item`] associated type is therefore bound on
19//! [`Geometry`] alone, so today's impls are expected to be
20//! homogeneous in practice (e.g. `Vec<Polygon<P>>`).
21
22use crate::geometry::Geometry;
23use geometry_tag::GeometryCollectionTag;
24
25/// A collection of geometries belonging to each other.
26///
27/// Mirrors the `GeometryCollection` concept; the canonical C++ model
28/// is `boost::geometry::model::geometry_collection` in
29/// `boost/geometry/geometries/geometry_collection.hpp`, tagged with
30/// `geometry_collection_tag` (`boost/geometry/core/tags.hpp`).
31///
32/// In v1 the [`Item`](Self::Item) associated type is bound only on
33/// [`Geometry`] — every concrete impl is homogeneous (a single
34/// element type for the whole collection). Heterogeneous dispatch is
35/// intentionally deferred to a later iteration; see
36/// `specs/FUTURE_ITERATIONS.md` §1.3 (`DynGeometry` variant) and
37/// §1.4 (heterogeneous `GeometryCollection`).
38///
39/// # Examples
40///
41/// ```
42/// use geometry_trait::GeometryCollection;
43/// fn count<C: GeometryCollection>(c: &C) -> usize { c.items().len() }
44/// ```
45pub trait GeometryCollection: Geometry<Kind = GeometryCollectionTag> {
46    /// The element geometry type.
47    ///
48    /// Mirrors the `DynamicGeometry` template parameter on
49    /// `boost::geometry::model::geometry_collection<DynamicGeometry, …>`
50    /// (`boost/geometry/geometries/geometry_collection.hpp`). In v1
51    /// the bound is just [`Geometry`]; once §1.4 lands this will
52    /// tighten to a dynamic-geometry concept.
53    type Item: Geometry;
54
55    /// The items of this collection, in declared order.
56    ///
57    /// Plays the role of `boost::begin(gc)` / `boost::end(gc)` from
58    /// `boost/geometry/geometries/geometry_collection.hpp` when read
59    /// together.
60    fn items(&self) -> impl ExactSizeIterator<Item = &Self::Item>;
61}
62
63#[cfg(test)]
64mod tests {
65    extern crate alloc;
66
67    use super::*;
68    use crate::point::{Point, PointMut};
69    use alloc::vec;
70    use alloc::vec::Vec;
71    use geometry_cs::Cartesian;
72    use geometry_tag::PointTag;
73
74    // Witness: any T satisfying the trait is accepted. Static,
75    // compile-time check; never runs.
76    fn accepts_gc<G: GeometryCollection>() {}
77
78    // Shared 2D Cartesian point used by the test impl below.
79    struct Xy(f64, f64);
80
81    impl Geometry for Xy {
82        type Kind = PointTag;
83        type Point = Self;
84    }
85
86    impl Point for Xy {
87        type Scalar = f64;
88        type Cs = Cartesian;
89        const DIM: usize = 2;
90
91        fn get<const D: usize>(&self) -> f64 {
92            if D == 0 { self.0 } else { self.1 }
93        }
94    }
95
96    impl PointMut for Xy {
97        fn set<const D: usize>(&mut self, v: f64) {
98            if D == 0 {
99                self.0 = v;
100            } else {
101                self.1 = v;
102            }
103        }
104    }
105
106    // Homogeneous Vec-backed collection of points.
107    struct ManyPoints(Vec<Xy>);
108
109    impl Geometry for ManyPoints {
110        type Kind = GeometryCollectionTag;
111        type Point = Xy;
112    }
113
114    impl GeometryCollection for ManyPoints {
115        type Item = Xy;
116
117        fn items(&self) -> impl ExactSizeIterator<Item = &Xy> {
118            self.0.iter()
119        }
120    }
121
122    #[test]
123    fn collection_iterates_all_items() {
124        let m = ManyPoints(vec![Xy(0.0, 0.0), Xy(1.0, 1.0), Xy(2.0, 2.0)]);
125        accepts_gc::<ManyPoints>();
126        assert_eq!(m.items().len(), 3);
127        let xs: Vec<f64> = m.items().map(Xy::get::<0>).collect();
128        assert_eq!(xs, vec![0.0, 1.0, 2.0]);
129    }
130}
geometry_trait/collection.rs

geometry_trait/
collection.rs
